{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89651", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.742Z", "datePublished": "2026-09-11T19:45:41.620Z", "dateUpdated": "2026-10-19T08:50:22.893Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:50:22.893Z" }, "descriptions": [ { "lang": "en", "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 >= 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() ->\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." } ], "metrics": [ { "cvssV3_1": { "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" }, "scenarios": [ { "lang": "en", "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->hdr.version and the MDSCapAuth path/fs_name u32 lengths; setting version>=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's 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'd 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." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/ceph/mds_client.c" ], "versions": [ { "version": "1d17de9534cb5a4c4c380d174cc2f9281b34f89e", "lessThan": "dc5c7dffda92ef372fa587c444a1c537373df824", "status": "affected", "versionType": "git" }, { "version": "1d17de9534cb5a4c4c380d174cc2f9281b34f89e", "lessThan": "c37db86d2b5e9b57001ccae7e7a727e95a4f9c02", "status": "affected", "versionType": "git" }, { "version": "1d17de9534cb5a4c4c380d174cc2f9281b34f89e", "lessThan": "5f892c767b30e4fb0c744c59f9235c717383d2cd", "status": "affected", "versionType": "git" }, { "version": "1d17de9534cb5a4c4c380d174cc2f9281b34f89e", "lessThan": "77933e22adfe813be2bd10be08d6e950103c3967", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "fs/ceph/mds_client.c" ], "versions": [ { "version": "6.10", "status": "affected" }, { "version": "0", "lessThan": "6.10", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.109", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.50", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.4", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/dc5c7dffda92ef372fa587c444a1c537373df824" }, { "url": "https://git.kernel.org/stable/c/c37db86d2b5e9b57001ccae7e7a727e95a4f9c02" }, { "url": "https://git.kernel.org/stable/c/5f892c767b30e4fb0c744c59f9235c717383d2cd" }, { "url": "https://git.kernel.org/stable/c/77933e22adfe813be2bd10be08d6e950103c3967" } ], "title": "ceph: bound MDSCapAuth path and fs_name decode in handle_session()", "x_generator": { "engine": "bippy-1.2.0" } } } }