GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

CVE-2026-89654 (GCVE-0-2026-89654)

Vulnerability from cvelistv5 – Published: 2026-09-11 19:45 – Updated: 2026-09-13 06:32
VLAI
Title
ceph: fix UAF in check_new_map() on session freed during unlock
Summary
In the Linux kernel, the following vulnerability has been resolved: ceph: fix UAF in check_new_map() on session freed during unlock check_new_map() iterates mdsc->sessions[] and for each active session drops mdsc->mutex to perform per-session operations. The forced-close path (rank removed from map) correctly takes a reference on s via ceph_get_mds_session() before releasing mdsc->mutex, but three other paths do not: Path A (address changed): mutex_unlock → mutex_lock(&s->s_mutex) Path B (reconnect): mutex_unlock → send_mds_reconnect(mdsc, s) Path C (active transition): mutex_unlock → mutex_lock(&s->s_mutex) Without the extra reference, another thread can acquire mdsc->mutex during the unlock window, call __unregister_session() which drops the last reference on s, and free it. The original thread then accesses freed memory via s->s_mutex. Fix by adding ceph_get_mds_session(s) before each mutex_unlock and ceph_put_mds_session(s) after the corresponding mutex_lock, matching the pattern already used in the forced-close path. Race timeline (Path A): Thread A (check_new_map) Thread B (another map update holds mdsc->mutex or session teardown) -------------------------- -------------------------- s = mdsc->sessions[i] (refcount == 1, held only by sessions[] array) mutex_unlock(&mdsc->mutex) ---> acquires mdsc->mutex __unregister_session(mdsc, s) sessions[i] = NULL ceph_put_mds_session(s) refcount: 1 -> 0 kfree(s) <--- freed! mutex_lock(&s->s_mutex) UAF on freed s->s_mutex
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: 2f2dc053404febedc9c273452d9d518fb31fde72 , < 21d5be092d947f8d83f76f7ebf3989e7e9230a98 (git)
Affected: 2f2dc053404febedc9c273452d9d518fb31fde72 , < ee611a7509554c4ca1f54f6aefe592fb1df7ea70 (git)
guessed Create a notification for this product.
Linux Linux Affected: 2.6.34
Unaffected: 0 , < 2.6.34 (semver)
Unaffected: 7.2.4 , ≤ 7.2.* (semver)
Unaffected: 7.3-rc1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "fs/ceph/mds_client.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "21d5be092d947f8d83f76f7ebf3989e7e9230a98",
              "status": "affected",
              "version": "2f2dc053404febedc9c273452d9d518fb31fde72",
              "versionType": "git"
            },
            {
              "lessThan": "ee611a7509554c4ca1f54f6aefe592fb1df7ea70",
              "status": "affected",
              "version": "2f2dc053404febedc9c273452d9d518fb31fde72",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "fs/ceph/mds_client.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "2.6.34"
            },
            {
              "lessThan": "2.6.34",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.2.*",
              "status": "unaffected",
              "version": "7.2.4",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.3-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2.4",
                  "versionStartIncluding": "2.6.34",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.3-rc1",
                  "versionStartIncluding": "2.6.34",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nceph: fix UAF in check_new_map() on session freed during unlock\n\ncheck_new_map() iterates mdsc-\u003esessions[] and for each active session\ndrops mdsc-\u003emutex to perform per-session operations.  The forced-close\npath (rank removed from map) correctly takes a reference on s via\nceph_get_mds_session() before releasing mdsc-\u003emutex, but three other\npaths do not:\n\n  Path A (address changed):  mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\n  Path B (reconnect):        mutex_unlock \u2192 send_mds_reconnect(mdsc, s)\n  Path C (active transition): mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\n\nWithout the extra reference, another thread can acquire mdsc-\u003emutex\nduring the unlock window, call __unregister_session() which drops the\nlast reference on s, and free it.  The original thread then accesses\nfreed memory via s-\u003es_mutex.\n\nFix by adding ceph_get_mds_session(s) before each mutex_unlock and\nceph_put_mds_session(s) after the corresponding mutex_lock, matching\nthe pattern already used in the forced-close path.\n\nRace timeline (Path A):\n\n  Thread A (check_new_map)             Thread B (another map update\n    holds mdsc-\u003emutex                      or session teardown)\n  --------------------------           --------------------------\n  s = mdsc-\u003esessions[i]\n  (refcount == 1, held only by\n   sessions[] array)\n\n  mutex_unlock(\u0026mdsc-\u003emutex)\n                               ---\u003e    acquires mdsc-\u003emutex\n                                       __unregister_session(mdsc, s)\n                                         sessions[i] = NULL\n                                         ceph_put_mds_session(s)\n                                           refcount: 1 -\u003e 0\n                                           kfree(s)  \u003c--- freed!\n\n  mutex_lock(\u0026s-\u003es_mutex)\n  UAF on freed s-\u003es_mutex"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - check_new_map() runs from ceph_mdsc_handle_mdsmap() on CEPH_MSG_MDS_MAP received over TCP from a monitor (extra_mon_dispatch) or MDS (mds_dispatch); a malicious or compromised Ceph peer reaches the UAF on already-mounted CephFS clients without a local syscall.\nAC:L - A cluster attacker controls both race sides: one TCP session delivers an MDS map that drops mdsc-\u003emutex in the address-change, reconnect, or active-transition paths, while another concurrently sends a rank-removing map, CEPH_SESSION_CLOSE, or connection reset into __unregister_session(); Path B\u0027s send_mds_reconnect() GFP_NOFS work makes the window retryable.\nPR:N - The attacker acts as the remote MON/MDS peer, or an on-path attacker on a legacy unsigned msgr session, and needs no UID, capability, or init-namespace root on the victim; any kernel CephFS client already connected to that cluster is exposed.\nUI:N - Once CephFS is mounted, as is standard on Rook/Kubernetes, HPC, and cloud nodes, MDS-map updates and session teardown messages are processed automatically in ceph-msgr kworker context with no further victim mount, open, or interactive action.\nS:U - The session-object use-after-free corrupts kernel heap on the client host within the same security authority and does not inherently cross a VM, IOMMU, or sandbox boundary.\nC:H - Use-after-free of struct ceph_mds_session allows reclaim of the freed object so later reads of session fields, embedded connection state, and cap lists can disclose arbitrary kernel memory, matching CNA guidance that UAFs enable high confidentiality impact.\nI:H - The same reclaimed session is written (s_mutex, s_state, ceph_con_close, reconnect and cap-kick paths), enabling heap corruption and hijack of the embedded ceph_connection ops for arbitrary kernel writes and control-flow hijacking.\nA:H - Locking or dereferencing the freed session mutex and fields causes a kernel oops or panic, and the attacker can repeat map updates and session teardown to trigger the crash."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-09-13T06:32:34.380Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/21d5be092d947f8d83f76f7ebf3989e7e9230a98"
        },
        {
          "url": "https://git.kernel.org/stable/c/ee611a7509554c4ca1f54f6aefe592fb1df7ea70"
        }
      ],
      "title": "ceph: fix UAF in check_new_map() on session freed during unlock",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-89654",
    "datePublished": "2026-09-11T19:45:44.086Z",
    "dateReserved": "2026-09-11T19:38:34.743Z",
    "dateUpdated": "2026-09-13T06:32:34.380Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-89654",
      "date": "2026-09-15",
      "epss": "0.00407",
      "percentile": "0.34317"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-89654\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-09-11T20:19:51.540\",\"lastModified\":\"2026-09-13T07:17:30.837\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nceph: fix UAF in check_new_map() on session freed during unlock\\n\\ncheck_new_map() iterates mdsc-\u003esessions[] and for each active session\\ndrops mdsc-\u003emutex to perform per-session operations.  The forced-close\\npath (rank removed from map) correctly takes a reference on s via\\nceph_get_mds_session() before releasing mdsc-\u003emutex, but three other\\npaths do not:\\n\\n  Path A (address changed):  mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\\n  Path B (reconnect):        mutex_unlock \u2192 send_mds_reconnect(mdsc, s)\\n  Path C (active transition): mutex_unlock \u2192 mutex_lock(\u0026s-\u003es_mutex)\\n\\nWithout the extra reference, another thread can acquire mdsc-\u003emutex\\nduring the unlock window, call __unregister_session() which drops the\\nlast reference on s, and free it.  The original thread then accesses\\nfreed memory via s-\u003es_mutex.\\n\\nFix by adding ceph_get_mds_session(s) before each mutex_unlock and\\nceph_put_mds_session(s) after the corresponding mutex_lock, matching\\nthe pattern already used in the forced-close path.\\n\\nRace timeline (Path A):\\n\\n  Thread A (check_new_map)             Thread B (another map update\\n    holds mdsc-\u003emutex                      or session teardown)\\n  --------------------------           --------------------------\\n  s = mdsc-\u003esessions[i]\\n  (refcount == 1, held only by\\n   sessions[] array)\\n\\n  mutex_unlock(\u0026mdsc-\u003emutex)\\n                               ---\u003e    acquires mdsc-\u003emutex\\n                                       __unregister_session(mdsc, s)\\n                                         sessions[i] = NULL\\n                                         ceph_put_mds_session(s)\\n                                           refcount: 1 -\u003e 0\\n                                           kfree(s)  \u003c--- freed!\\n\\n  mutex_lock(\u0026s-\u003es_mutex)\\n  UAF on freed s-\u003es_mutex\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/ceph/mds_client.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2f2dc053404febedc9c273452d9d518fb31fde72\",\"lessThan\":\"21d5be092d947f8d83f76f7ebf3989e7e9230a98\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"2f2dc053404febedc9c273452d9d518fb31fde72\",\"lessThan\":\"ee611a7509554c4ca1f54f6aefe592fb1df7ea70\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/ceph/mds_client.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"2.6.34\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"2.6.34\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2.4\",\"lessThanOrEqual\":\"7.2.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.3-rc1\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/21d5be092d947f8d83f76f7ebf3989e7e9230a98\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/ee611a7509554c4ca1f54f6aefe592fb1df7ea70\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-09-14T16:47:13+00:00",
      "cve": "CVE-2026-89654",
      "id": "CVE-2026-89654",
      "initial_release_date": "2026-09-11T00:00:00+00:00",
      "product_status:known_affected": "262",
      "product_status:known_not_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ceph: fix UAF in check_new_map() on session freed during unlock",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89654.json",
      "version": "3"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





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

Author Source Type Date Other

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.