{"id":"CVE-2026-89651","state":"PUBLISHED","title":"ceph: bound MDSCapAuth path and fs_name decode in handle_session()","description":"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.","publishedAt":"2026-09-11T19:45:41.620Z","updatedAt":"2026-10-19T08:50:22.893Z","severity":{"score":9.8,"label":"Critical","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"dc5c7dffda92ef372fa587c444a1c537373df824","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"c37db86d2b5e9b57001ccae7e7a727e95a4f9c02","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"5f892c767b30e4fb0c744c59f9235c717383d2cd","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"77933e22adfe813be2bd10be08d6e950103c3967","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ceph/mds_client.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.10","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.10","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ceph/mds_client.c"]}],"references":["https://git.kernel.org/stable/c/dc5c7dffda92ef372fa587c444a1c537373df824","https://git.kernel.org/stable/c/c37db86d2b5e9b57001ccae7e7a727e95a4f9c02","https://git.kernel.org/stable/c/5f892c767b30e4fb0c744c59f9235c717383d2cd","https://git.kernel.org/stable/c/77933e22adfe813be2bd10be08d6e950103c3967"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89651.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89651","state":"PUBLISHED","datePublished":"2026-09-11T19:45:41.620Z","dateUpdated":"2026-10-19T08:50:22.893Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.742Z"},"containers":{"cna":{"title":"ceph: bound MDSCapAuth path and fs_name decode in handle_session()","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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"dc5c7dffda92ef372fa587c444a1c537373df824","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"c37db86d2b5e9b57001ccae7e7a727e95a4f9c02","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"5f892c767b30e4fb0c744c59f9235c717383d2cd","versionType":"git"},{"version":"1d17de9534cb5a4c4c380d174cc2f9281b34f89e","status":"affected","lessThan":"77933e22adfe813be2bd10be08d6e950103c3967","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ceph/mds_client.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"6.10","status":"affected"},{"version":"0","status":"unaffected","lessThan":"6.10","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ceph/mds_client.c"]}],"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"}],"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."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:50:22.893Z"},"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"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}