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CVE-2025-21796 (GCVE-0-2025-21796)

Vulnerability from cvelistv5 – Published: 2025-02-27 02:18 – Updated: 2026-09-08 08:40
VLAI
Title
nfsd: clear acl_access/acl_default after releasing them
Summary
In the Linux kernel, the following vulnerability has been resolved: nfsd: clear acl_access/acl_default after releasing them If getting acl_default fails, acl_access and acl_default will be released simultaneously. However, acl_access will still retain a pointer pointing to the released posix_acl, which will trigger a WARNING in nfs3svc_release_getacl like this: ------------[ cut here ]------------ refcount_t: underflow; use-after-free. WARNING: CPU: 26 PID: 3199 at lib/refcount.c:28 refcount_warn_saturate+0xb5/0x170 Modules linked in: CPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted 6.12.0-rc6-00079-g04ae226af01f-dirty #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:refcount_warn_saturate+0xb5/0x170 Code: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75 e4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff <0f> 0b eb cd 0f b6 1d 8a3 RSP: 0018:ffffc90008637cd8 EFLAGS: 00010282 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380 RBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56 R10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001 R13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0 FS: 0000000000000000(0000) GS:ffff88871ed00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace: <TASK> ? refcount_warn_saturate+0xb5/0x170 ? __warn+0xa5/0x140 ? refcount_warn_saturate+0xb5/0x170 ? report_bug+0x1b1/0x1e0 ? handle_bug+0x53/0xa0 ? exc_invalid_op+0x17/0x40 ? asm_exc_invalid_op+0x1a/0x20 ? tick_nohz_tick_stopped+0x1e/0x40 ? refcount_warn_saturate+0xb5/0x170 ? refcount_warn_saturate+0xb5/0x170 nfs3svc_release_getacl+0xc9/0xe0 svc_process_common+0x5db/0xb60 ? __pfx_svc_process_common+0x10/0x10 ? __rcu_read_unlock+0x69/0xa0 ? __pfx_nfsd_dispatch+0x10/0x10 ? svc_xprt_received+0xa1/0x120 ? xdr_init_decode+0x11d/0x190 svc_process+0x2a7/0x330 svc_handle_xprt+0x69d/0x940 svc_recv+0x180/0x2d0 nfsd+0x168/0x200 ? __pfx_nfsd+0x10/0x10 kthread+0x1a2/0x1e0 ? kthread+0xf4/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x34/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30 </TASK> Kernel panic - not syncing: kernel: panic_on_warn set ... Clear acl_access/acl_default after posix_acl_release is called to prevent UAF from being triggered.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2025-02-27 17:57 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 8a1737ae42c928384ab6447f6ee1a882510e85fa (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 6f7cfee1a316891890c505563aa54f3476db52fd (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 2e59b2b68782519560b3d6a41dd66a3d01a01cd3 (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 55d947315fb5f67a35e4e1d3e01bb886b9c6decf (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < f8d871523142f7895f250a856f8c4a4181614510 (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 1fd94884174bd20beb1773990fd3b1aa877688d9 (git)
Affected: a257cdd0e2179630d3201c32ba14d7fcb3c3a055 , < 7faf14a7b0366f153284db0ad3347c457ea70136 (git)
guessed Create a notification for this product.
Linux Linux Affected: 2.6.13
Unaffected: 0 , < 2.6.13 (semver)
Unaffected: 5.10.235 , ≤ 5.10.* (semver)
Unaffected: 5.15.179 , ≤ 5.15.* (semver)
Unaffected: 6.1.129 , ≤ 6.1.* (semver)
Unaffected: 6.6.79 , ≤ 6.6.* (semver)
Unaffected: 6.12.16 , ≤ 6.12.* (semver)
Unaffected: 6.13.4 , ≤ 6.13.* (semver)
Unaffected: 6.14 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem Affected: 0 , < * (custom)
guessed Create a notification for this product.
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.5 , < * (custom)
guessed Create a notification for this product.
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP Affected: V3.1.6 , < * (custom)
guessed Create a notification for this product.
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnfsd: clear acl_access/acl_default after releasing them\n\nIf getting acl_default fails, acl_access and acl_default will be released\nsimultaneously. However, acl_access will still retain a pointer pointing\nto the released posix_acl, which will trigger a WARNING in\nnfs3svc_release_getacl like this:\n\n------------[ cut here ]------------\nrefcount_t: underflow; use-after-free.\nWARNING: CPU: 26 PID: 3199 at lib/refcount.c:28\nrefcount_warn_saturate+0xb5/0x170\nModules linked in:\nCPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted\n6.12.0-rc6-00079-g04ae226af01f-dirty #8\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS\n1.16.1-2.fc37 04/01/2014\nRIP: 0010:refcount_warn_saturate+0xb5/0x170\nCode: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75\ne4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff \u003c0f\u003e 0b eb\ncd 0f b6 1d 8a3\nRSP: 0018:ffffc90008637cd8 EFLAGS: 00010282\nRAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde\nRDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380\nRBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56\nR10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001\nR13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0\nFS:  0000000000000000(0000) GS:ffff88871ed00000(0000)\nknlGS:0000000000000000\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\nCR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0\nDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\nDR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\nCall Trace:\n \u003cTASK\u003e\n ? refcount_warn_saturate+0xb5/0x170\n ? __warn+0xa5/0x140\n ? refcount_warn_saturate+0xb5/0x170\n ? report_bug+0x1b1/0x1e0\n ? handle_bug+0x53/0xa0\n ? exc_invalid_op+0x17/0x40\n ? asm_exc_invalid_op+0x1a/0x20\n ? tick_nohz_tick_stopped+0x1e/0x40\n ? refcount_warn_saturate+0xb5/0x170\n ? refcount_warn_saturate+0xb5/0x170\n nfs3svc_release_getacl+0xc9/0xe0\n svc_process_common+0x5db/0xb60\n ? __pfx_svc_process_common+0x10/0x10\n ? __rcu_read_unlock+0x69/0xa0\n ? __pfx_nfsd_dispatch+0x10/0x10\n ? svc_xprt_received+0xa1/0x120\n ? xdr_init_decode+0x11d/0x190\n svc_process+0x2a7/0x330\n svc_handle_xprt+0x69d/0x940\n svc_recv+0x180/0x2d0\n nfsd+0x168/0x200\n ? __pfx_nfsd+0x10/0x10\n kthread+0x1a2/0x1e0\n ? kthread+0xf4/0x1e0\n ? __pfx_kthread+0x10/0x10\n ret_from_fork+0x34/0x60\n ? __pfx_kthread+0x10/0x10\n ret_from_fork_asm+0x1a/0x30\n \u003c/TASK\u003e\nKernel panic - not syncing: kernel: panic_on_warn set ...\n\nClear acl_access/acl_default after posix_acl_release is called to prevent\nUAF from being triggered."
        }
      ],
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            {
              "lang": "en",
              "value": "AV:N - The vulnerable functions are the NFSACL sideband RPC handlers (program 100227, ACLPROC2/3_GETACL) served by the in-kernel nfsd on port 2049; a remote NFS client reaches them purely by sending a GETACL call with a filehandle and a mask.\nAC:L - The attacker fully controls the mask field that selects both the access and default ACL branches, and can retry indefinitely; the error condition is deterministic on FUSE-backed exports and on any file with a malformed/corrupt system.posix_acl_default xattr, and is otherwise reachable via the unlocked -ERANGE window in ext4_get_acl that the attacker drives from both sides with concurrent SETACL/GETACL.\nPR:N - NFS AUTH_SYS performs no real authentication \u2014 the client merely asserts a uid \u2014 and fh_verify() is called with NFSD_MAY_NOP, so nfsd_permission() returns 0 without any file ownership or mode check; any host permitted by the export list can issue GETACL against any object in the export.\nUI:N - The entire sequence is driven by attacker-sent RPC calls handled by the nfsd kernel threads; no action by a local user or administrator is required.\nS:U - The freed posix_acl, the dangling inode-\u003ei_acl, and the resulting corruption all reside in the kernel\u0027s own security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - In the NFSv2-ACL encoder the released posix_acl is still passed to nfs_stream_encode_acl(), which reads a_count and up to 1024 a_entries[] from the freed slab object and transmits them to the remote client, yielding freed-heap disclosure plus a large out-of-bounds read; the cached-ACL variant additionally leaves inode-\u003ei_acl dangling for later reads.\nI:H - The second posix_acl_release() performs an atomic decrement into freed (potentially reallocated) slab memory, and in the cached case the dangling inode-\u003ei_acl leads to refcount_inc on freed memory, a genuine double free on the next set/forget_cached_acl, and posix_acl_permission() making file access-control decisions from attacker-groomable freed heap contents.\nA:H - The bug reproduces as a refcount_t underflow WARN in nfs3svc_release_getacl (kernel panic with panic_on_warn, as shown in the commit\u0027s own report), and the use-after-free of a slab object causes further corruption and oopses; it is remotely and repeatedly triggerable."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T11:54:31.388Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/8a1737ae42c928384ab6447f6ee1a882510e85fa"
        },
        {
          "url": "https://git.kernel.org/stable/c/6f7cfee1a316891890c505563aa54f3476db52fd"
        },
        {
          "url": "https://git.kernel.org/stable/c/2e59b2b68782519560b3d6a41dd66a3d01a01cd3"
        },
        {
          "url": "https://git.kernel.org/stable/c/55d947315fb5f67a35e4e1d3e01bb886b9c6decf"
        },
        {
          "url": "https://git.kernel.org/stable/c/f8d871523142f7895f250a856f8c4a4181614510"
        },
        {
          "url": "https://git.kernel.org/stable/c/1fd94884174bd20beb1773990fd3b1aa877688d9"
        },
        {
          "url": "https://git.kernel.org/stable/c/7faf14a7b0366f153284db0ad3347c457ea70136"
        }
      ],
      "title": "nfsd: clear acl_access/acl_default after releasing them",
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        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-21796",
    "datePublished": "2025-02-27T02:18:32.191Z",
    "dateReserved": "2024-12-29T08:45:45.768Z",
    "dateUpdated": "2026-09-08T08:40:39.049Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2025-21796",
      "date": "2026-09-16",
      "epss": "0.00635",
      "percentile": "0.48784"
    },
    "microsoft_vex": {
      "current_release_date": "2026-02-18T15:07:25.000Z",
      "cve": "CVE-2025-21796",
      "id": "msrc_CVE-2025-21796",
      "initial_release_date": "2025-02-02T00:00:00.000Z",
      "product_status:fixed": "5",
      "product_status:known_affected": "5",
      "source": "Microsoft CSAF VEX",
      "status": "final",
      "title": "nfsd: clear acl_access/acl_default after releasing them",
      "url": "https://msrc.microsoft.com/csaf/vex/2025/msrc_cve-2025-21796.json",
      "version": "3"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-21796\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-02-27T03:15:20.497\",\"lastModified\":\"2026-07-30T06:21:31.720\",\"vulnStatus\":\"Modified\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnfsd: clear acl_access/acl_default after releasing them\\n\\nIf getting acl_default fails, acl_access and acl_default will be released\\nsimultaneously. However, acl_access will still retain a pointer pointing\\nto the released posix_acl, which will trigger a WARNING in\\nnfs3svc_release_getacl like this:\\n\\n------------[ cut here ]------------\\nrefcount_t: underflow; use-after-free.\\nWARNING: CPU: 26 PID: 3199 at lib/refcount.c:28\\nrefcount_warn_saturate+0xb5/0x170\\nModules linked in:\\nCPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted\\n6.12.0-rc6-00079-g04ae226af01f-dirty #8\\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS\\n1.16.1-2.fc37 04/01/2014\\nRIP: 0010:refcount_warn_saturate+0xb5/0x170\\nCode: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75\\ne4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff \u003c0f\u003e 0b eb\\ncd 0f b6 1d 8a3\\nRSP: 0018:ffffc90008637cd8 EFLAGS: 00010282\\nRAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde\\nRDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380\\nRBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56\\nR10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001\\nR13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0\\nFS:  0000000000000000(0000) GS:ffff88871ed00000(0000)\\nknlGS:0000000000000000\\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\\nCR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0\\nDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\\nDR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\\nCall Trace:\\n \u003cTASK\u003e\\n ? refcount_warn_saturate+0xb5/0x170\\n ? __warn+0xa5/0x140\\n ? refcount_warn_saturate+0xb5/0x170\\n ? report_bug+0x1b1/0x1e0\\n ? handle_bug+0x53/0xa0\\n ? exc_invalid_op+0x17/0x40\\n ? asm_exc_invalid_op+0x1a/0x20\\n ? tick_nohz_tick_stopped+0x1e/0x40\\n ? refcount_warn_saturate+0xb5/0x170\\n ? refcount_warn_saturate+0xb5/0x170\\n nfs3svc_release_getacl+0xc9/0xe0\\n svc_process_common+0x5db/0xb60\\n ? __pfx_svc_process_common+0x10/0x10\\n ? __rcu_read_unlock+0x69/0xa0\\n ? __pfx_nfsd_dispatch+0x10/0x10\\n ? svc_xprt_received+0xa1/0x120\\n ? xdr_init_decode+0x11d/0x190\\n svc_process+0x2a7/0x330\\n svc_handle_xprt+0x69d/0x940\\n svc_recv+0x180/0x2d0\\n nfsd+0x168/0x200\\n ? __pfx_nfsd+0x10/0x10\\n kthread+0x1a2/0x1e0\\n ? kthread+0xf4/0x1e0\\n ? __pfx_kthread+0x10/0x10\\n ret_from_fork+0x34/0x60\\n ? __pfx_kthread+0x10/0x10\\n ret_from_fork_asm+0x1a/0x30\\n \u003c/TASK\u003e\\nKernel panic - not syncing: kernel: panic_on_warn set ...\\n\\nClear acl_access/acl_default after posix_acl_release is called to prevent\\nUAF from being triggered.\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: nfsd: borrar acl_access/acl_default despu\u00e9s de liberarlos Si la obtenci\u00f3n de acl_default falla, acl_access y acl_default se liberar\u00e1n simult\u00e1neamente. Sin embargo, acl_access a\u00fan conservar\u00e1 un puntero que apunta al posix_acl liberado, lo que activar\u00e1 una ADVERTENCIA en nfs3svc_release_getacl como esta: ------------[ cortar aqu\u00ed ]------------ refcount_t: desbordamiento insuficiente; use after free. ADVERTENCIA: CPU: 26 PID: 3199 at lib/refcount.c:28 refcount_warn_saturate+0xb5/0x170 Modules linked in: CPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted 6.12.0-rc6-00079-g04ae226af01f-dirty #8 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.1-2.fc37 04/01/2014 RIP: 0010:refcount_warn_saturate+0xb5/0x170 Code: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75 e4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff \u0026lt;0f\u0026gt; 0b eb cd 0f b6 1d 8a3 RSP: 0018:ffffc90008637cd8 EFLAGS: 00010282 RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde RDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380 RBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56 R10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001 R13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0 FS: 0000000000000000(0000) GS:ffff88871ed00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 Call Trace:  ? refcount_warn_saturate+0xb5/0x170 ? __warn+0xa5/0x140 ? refcount_warn_saturate+0xb5/0x170 ? report_bug+0x1b1/0x1e0 ? handle_bug+0x53/0xa0 ? exc_invalid_op+0x17/0x40 ? asm_exc_invalid_op+0x1a/0x20 ? tick_nohz_tick_stopped+0x1e/0x40 ? refcount_warn_saturate+0xb5/0x170 ? refcount_warn_saturate+0xb5/0x170 nfs3svc_release_getacl+0xc9/0xe0 svc_process_common+0x5db/0xb60 ? __pfx_svc_process_common+0x10/0x10 ? __rcu_read_unlock+0x69/0xa0 ? __pfx_nfsd_dispatch+0x10/0x10 ? svc_xprt_received+0xa1/0x120 ? xdr_init_decode+0x11d/0x190 svc_process+0x2a7/0x330 svc_handle_xprt+0x69d/0x940 svc_recv+0x180/0x2d0 nfsd+0x168/0x200 ? __pfx_nfsd+0x10/0x10 kthread+0x1a2/0x1e0 ? kthread+0xf4/0x1e0 ? __pfx_kthread+0x10/0x10 ret_from_fork+0x34/0x60 ? __pfx_kthread+0x10/0x10 ret_from_fork_asm+0x1a/0x30  Kernel panic - not syncing: kernel: panic_on_warn set ...  Borre acl_access/acl_default despu\u00e9s de llamar a posix_acl_release para evitar que se active UAF.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/nfsd/nfs2acl.c\",\"fs/nfsd/nfs3acl.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"8a1737ae42c928384ab6447f6ee1a882510e85fa\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"6f7cfee1a316891890c505563aa54f3476db52fd\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"2e59b2b68782519560b3d6a41dd66a3d01a01cd3\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"55d947315fb5f67a35e4e1d3e01bb886b9c6decf\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"f8d871523142f7895f250a856f8c4a4181614510\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"1fd94884174bd20beb1773990fd3b1aa877688d9\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\",\"lessThan\":\"7faf14a7b0366f153284db0ad3347c457ea70136\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/nfsd/nfs2acl.c\",\"fs/nfsd/nfs3acl.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.13\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.13\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.10.235\",\"lessThanOrEqual\":\"5.10.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"5.15.179\",\"lessThanOrEqual\":\"5.15.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.1.129\",\"lessThanOrEqual\":\"6.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.6.79\",\"lessThanOrEqual\":\"6.6.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.16\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.13.4\",\"lessThanOrEqual\":\"6.13.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.14\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]},{\"source\":\"0b142b55-0307-4c5a-b3c9-f314f3fb7c5e\",\"affectedData\":[{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.5\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.6\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.5\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.6\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.5\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.6\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.5\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP\",\"defaultStatus\":\"unknown\",\"versions\":[{\"version\":\"V3.1.6\",\"lessThan\":\"*\",\"versionType\":\"custom\",\"status\":\"affected\"}]},{\"vendor\":\"Siemens\",\"product\":\"SIMATIC S7-1500 TM MFP - GNU/Linux 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a remote NFS client reaches them purely by sending a GETACL call with a filehandle and a mask.\\nAC:L - The attacker fully controls the mask field that selects both the access and default ACL branches, and can retry indefinitely; the error condition is deterministic on FUSE-backed exports and on any file with a malformed/corrupt system.posix_acl_default xattr, and is otherwise reachable via the unlocked -ERANGE window in ext4_get_acl that the attacker drives from both sides with concurrent SETACL/GETACL.\\nPR:N - NFS AUTH_SYS performs no real authentication \\u2014 the client merely asserts a uid \\u2014 and fh_verify() is called with NFSD_MAY_NOP, so nfsd_permission() returns 0 without any file ownership or mode check; any host permitted by the export list can issue GETACL against any object in the export.\\nUI:N - The entire sequence is driven by attacker-sent RPC calls handled by the nfsd kernel threads; no action by a local user or administrator is required.\\nS:U - The freed posix_acl, the dangling inode-\u003ei_acl, and the resulting corruption all reside in the kernel\u0027s own security authority; no VM, IOMMU, or sandbox boundary is crossed.\\nC:H - In the NFSv2-ACL encoder the released posix_acl is still passed to nfs_stream_encode_acl(), which reads a_count and up to 1024 a_entries[] from the freed slab object and transmits them to the remote client, yielding freed-heap disclosure plus a large out-of-bounds read; the cached-ACL variant additionally leaves inode-\u003ei_acl dangling for later reads.\\nI:H - The second posix_acl_release() performs an atomic decrement into freed (potentially reallocated) slab memory, and in the cached case the dangling inode-\u003ei_acl leads to refcount_inc on freed memory, a genuine double free on the next set/forget_cached_acl, and posix_acl_permission() making file access-control decisions from attacker-groomable freed heap contents.\\nA:H - The bug reproduces as a refcount_t underflow WARN in nfs3svc_release_getacl (kernel panic with panic_on_warn, as shown in the commit\u0027s own report), and the use-after-free of a slab object causes further corruption and oopses; it is remotely and repeatedly triggerable.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"8a1737ae42c928384ab6447f6ee1a882510e85fa\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"6f7cfee1a316891890c505563aa54f3476db52fd\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"2e59b2b68782519560b3d6a41dd66a3d01a01cd3\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"55d947315fb5f67a35e4e1d3e01bb886b9c6decf\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"f8d871523142f7895f250a856f8c4a4181614510\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"1fd94884174bd20beb1773990fd3b1aa877688d9\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"a257cdd0e2179630d3201c32ba14d7fcb3c3a055\", \"lessThan\": \"7faf14a7b0366f153284db0ad3347c457ea70136\", \"versionType\": \"git\"}], \"programFiles\": [\"fs/nfsd/nfs2acl.c\", \"fs/nfsd/nfs3acl.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"2.6.13\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"2.6.13\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.235\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.179\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.129\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.79\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.16\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.13.4\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.13.*\"}, {\"status\": \"unaffected\", \"version\": \"6.14\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"fs/nfsd/nfs2acl.c\", \"fs/nfsd/nfs3acl.c\"], \"defaultStatus\": \"affected\"}], \"references\": [{\"url\": \"https://git.kernel.org/stable/c/8a1737ae42c928384ab6447f6ee1a882510e85fa\"}, {\"url\": \"https://git.kernel.org/stable/c/6f7cfee1a316891890c505563aa54f3476db52fd\"}, {\"url\": \"https://git.kernel.org/stable/c/2e59b2b68782519560b3d6a41dd66a3d01a01cd3\"}, {\"url\": \"https://git.kernel.org/stable/c/55d947315fb5f67a35e4e1d3e01bb886b9c6decf\"}, {\"url\": \"https://git.kernel.org/stable/c/f8d871523142f7895f250a856f8c4a4181614510\"}, {\"url\": \"https://git.kernel.org/stable/c/1fd94884174bd20beb1773990fd3b1aa877688d9\"}, {\"url\": \"https://git.kernel.org/stable/c/7faf14a7b0366f153284db0ad3347c457ea70136\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnfsd: clear acl_access/acl_default after releasing them\\n\\nIf getting acl_default fails, acl_access and acl_default will be released\\nsimultaneously. However, acl_access will still retain a pointer pointing\\nto the released posix_acl, which will trigger a WARNING in\\nnfs3svc_release_getacl like this:\\n\\n------------[ cut here ]------------\\nrefcount_t: underflow; use-after-free.\\nWARNING: CPU: 26 PID: 3199 at lib/refcount.c:28\\nrefcount_warn_saturate+0xb5/0x170\\nModules linked in:\\nCPU: 26 UID: 0 PID: 3199 Comm: nfsd Not tainted\\n6.12.0-rc6-00079-g04ae226af01f-dirty #8\\nHardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS\\n1.16.1-2.fc37 04/01/2014\\nRIP: 0010:refcount_warn_saturate+0xb5/0x170\\nCode: cc cc 0f b6 1d b3 20 a5 03 80 fb 01 0f 87 65 48 d8 00 83 e3 01 75\\ne4 48 c7 c7 c0 3b 9b 85 c6 05 97 20 a5 03 01 e8 fb 3e 30 ff \u003c0f\u003e 0b eb\\ncd 0f b6 1d 8a3\\nRSP: 0018:ffffc90008637cd8 EFLAGS: 00010282\\nRAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff83904fde\\nRDX: dffffc0000000000 RSI: 0000000000000008 RDI: ffff88871ed36380\\nRBP: ffff888158beeb40 R08: 0000000000000001 R09: fffff520010c6f56\\nR10: ffffc90008637ab7 R11: 0000000000000001 R12: 0000000000000001\\nR13: ffff888140e77400 R14: ffff888140e77408 R15: ffffffff858b42c0\\nFS:  0000000000000000(0000) GS:ffff88871ed00000(0000)\\nknlGS:0000000000000000\\nCS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033\\nCR2: 0000562384d32158 CR3: 000000055cc6a000 CR4: 00000000000006f0\\nDR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000\\nDR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400\\nCall Trace:\\n \u003cTASK\u003e\\n ? refcount_warn_saturate+0xb5/0x170\\n ? __warn+0xa5/0x140\\n ? refcount_warn_saturate+0xb5/0x170\\n ? report_bug+0x1b1/0x1e0\\n ? handle_bug+0x53/0xa0\\n ? exc_invalid_op+0x17/0x40\\n ? asm_exc_invalid_op+0x1a/0x20\\n ? tick_nohz_tick_stopped+0x1e/0x40\\n ? refcount_warn_saturate+0xb5/0x170\\n ? refcount_warn_saturate+0xb5/0x170\\n nfs3svc_release_getacl+0xc9/0xe0\\n svc_process_common+0x5db/0xb60\\n ? __pfx_svc_process_common+0x10/0x10\\n ? __rcu_read_unlock+0x69/0xa0\\n ? __pfx_nfsd_dispatch+0x10/0x10\\n ? svc_xprt_received+0xa1/0x120\\n ? xdr_init_decode+0x11d/0x190\\n svc_process+0x2a7/0x330\\n svc_handle_xprt+0x69d/0x940\\n svc_recv+0x180/0x2d0\\n nfsd+0x168/0x200\\n ? __pfx_nfsd+0x10/0x10\\n kthread+0x1a2/0x1e0\\n ? kthread+0xf4/0x1e0\\n ? __pfx_kthread+0x10/0x10\\n ret_from_fork+0x34/0x60\\n ? __pfx_kthread+0x10/0x10\\n ret_from_fork_asm+0x1a/0x30\\n \u003c/TASK\u003e\\nKernel panic - not syncing: kernel: panic_on_warn set ...\\n\\nClear acl_access/acl_default after posix_acl_release is called to prevent\\nUAF from being triggered.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.235\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.179\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.129\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.79\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.16\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.13.4\", \"versionStartIncluding\": \"2.6.13\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.14\", \"versionStartIncluding\": \"2.6.13\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T11:54:31.388Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2025-21796\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-09-08T08:40:39.049Z\", \"dateReserved\": \"2024-12-29T08:45:45.768Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2025-02-27T02:18:32.191Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.