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CVE-2026-89651 (GCVE-0-2026-89651)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
ceph: bound MDSCapAuth path and fs_name decode in handle_session()
Summary
In the Linux kernel, the following vulnerability has been resolved: ceph: bound MDSCapAuth path and fs_name decode in handle_session() handle_session() decodes the MDSCapAuth records carried by a CEPH_SESSION_OPEN message (msg_version >= 6). For each record the match.path and match.fs_name byte strings are read by first decoding a 32-bit length and then copying that many bytes with the bare ceph_decode_copy(). Unlike the surrounding fields, which all use the _safe decode variants, these two copies are not preceded by a ceph_decode_need() bounds check, and the enclosing MDSCapAuth and MDSCapMatch struct_len fields are skipped rather than enforced as an upper bound. A length larger than the bytes remaining in the message front makes ceph_decode_copy() read past the end of the front buffer. The message front is a dedicated allocation (ceph_msg_new2() -> kvmalloc), so the over-read runs off that object. A malicious or compromised MDS can trigger this with the first post-connect message on mount, with no client-side user interaction; under KASAN it is reported as a slab-out-of-bounds read in handle_session(). Impact: a malicious MDS can force the kernel client to read up to 4 GiB past the message front allocation during session setup, crashing the client (out-of-bounds read). Switch both copies to ceph_decode_copy_safe(), which performs the ceph_decode_need() bounds check before the copy and branches to the existing bad label, matching the rest of the decoder and the error path that frees the partially decoded cap_auths array.
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1d17de9534cb5a4c4c380d174cc2f9281b34f89e , < dc5c7dffda92ef372fa587c444a1c537373df824 (git)
Affected: 1d17de9534cb5a4c4c380d174cc2f9281b34f89e , < c37db86d2b5e9b57001ccae7e7a727e95a4f9c02 (git)
Affected: 1d17de9534cb5a4c4c380d174cc2f9281b34f89e , < 5f892c767b30e4fb0c744c59f9235c717383d2cd (git)
Affected: 1d17de9534cb5a4c4c380d174cc2f9281b34f89e , < 77933e22adfe813be2bd10be08d6e950103c3967 (git)
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Linux Linux Affected: 6.10
Unaffected: 0 , < 6.10 (semver)
Unaffected: 6.12.109 , ≤ 6.12.* (semver)
Unaffected: 6.18.50 , ≤ 6.18.* (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
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{
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          "product": "Linux",
          "programFiles": [
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: bound MDSCapAuth path and fs_name decode in handle_session()\n\nhandle_session() decodes the MDSCapAuth records carried by a\nCEPH_SESSION_OPEN message (msg_version \u003e= 6). For each record the\nmatch.path and match.fs_name byte strings are read by first decoding a\n32-bit length and then copying that many bytes with the bare\nceph_decode_copy(). Unlike the surrounding fields, which all use the\n_safe decode variants, these two copies are not preceded by a\nceph_decode_need() bounds check, and the enclosing MDSCapAuth and\nMDSCapMatch struct_len fields are skipped rather than enforced as an\nupper bound. A length larger than the bytes remaining in the message\nfront makes ceph_decode_copy() read past the end of the front buffer.\n\nThe message front is a dedicated allocation (ceph_msg_new2() -\u003e\nkvmalloc), so the over-read runs off that object. A malicious or\ncompromised MDS can trigger this with the first post-connect message on\nmount, with no client-side user interaction; under KASAN it is reported\nas a slab-out-of-bounds read in handle_session().\n\nImpact: a malicious MDS can force the kernel client to read up to 4 GiB\npast the message front allocation during session setup, crashing the\nclient (out-of-bounds read).\n\nSwitch both copies to ceph_decode_copy_safe(), which performs the\nceph_decode_need() bounds check before the copy and branches to the\nexisting bad label, matching the rest of the decoder and the error path\nthat frees the partially decoded cap_auths array."
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            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
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              "value": "AV:N - CEPH_MSG_CLIENT_SESSION arrives over the kernel Ceph messenger TCP session from an MDS peer; mds_dispatch() hands it to handle_session(), so a malicious or compromised MDS (or on-path attacker on an unsigned msgr session) reaches the unbounded decode with network data alone.\nAC:L - The attacker fully controls msg-\u003ehdr.version and the MDSCapAuth path/fs_name u32 lengths; setting version\u003e=6 and a length larger than remaining front bytes (or UINT_MAX) deterministically hits the unchecked ceph_decode_copy() with no race or layout dependency.\nPR:N - Exploitation requires only sending a crafted CEPH_SESSION_OPEN as the remote MDS peer on an established session; the attacker needs no account, capability, or mount privilege on the victim beyond the client already being connected to that cluster.\nUI:N - Once CephFS is mounted (standard in Rook/Kubernetes/OpenStack), the MDS emits CEPH_SESSION_OPEN as the first post-connect message on mount or reconnect, processed automatically in the ceph-msgr kworker with no further victim action at exploit time.\nS:U - The out-of-bounds read and any resulting kernel memory corruption stay inside the victim host\u0027s CephFS client kernel; they do not cross a VM, sandbox, or IOMMU security boundary.\nC:H - Unchecked ceph_decode_copy() of an attacker-chosen u32 length reads past the kvmalloc\u0027d message front into adjacent kernel memory and stores those bytes in match.path/match.fs_name; unbounded out-of-bounds reads are High per kernel guidance.\nI:H - Attacker-controlled _len is both the memcpy size and kcalloc(_len+1) count, so UINT_MAX wraps the allocation to ZERO_SIZE_PTR and the copy writes from address 16; over-read bytes are also installed as cap-auth path/fs_name used by ceph_mds_check_access, a memory-corruption primitive.\nA:H - The over-read runs off the dedicated message-front object and can fault on unmapped pages or vmalloc guard pages, oopsing the ceph-msgr worker as KASAN reported; a malicious MDS can repeat this on every session open."
            }
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        "shortName": "Linux"
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89651",
    "datePublished": "2026-09-11T19:45:41.620Z",
    "dateReserved": "2026-09-11T19:38:34.742Z",
    "dateUpdated": "2026-09-13T06:32:30.623Z",
    "state": "PUBLISHED"
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      "date": "2026-09-15",
      "epss": "0.00626",
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    },
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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-09-13T06:51:09+00:00",
      "cve": "CVE-2026-89651",
      "id": "CVE-2026-89651",
      "initial_release_date": "2026-09-11T19:45:41.620000+00:00",
      "product_status:known_affected": "2",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ceph: Linux kernel Ceph client: Out-of-bounds read leads to denial of service",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89651.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "critical",
      "current_release_date": "2026-09-13T16:57:33Z",
      "cve": "CVE-2026-89651",
      "id": "CVE-2026-89651",
      "initial_release_date": "2026-09-12T16:24:15Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-89651",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-89651.json",
      "version": "3"
    }
  }
}



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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.