GHSA-VQXR-6XH4-GCCQ
Vulnerability from github – Published: 2026-09-11 21:31 – Updated: 2026-09-13 09:32In 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.
{
"affected": [],
"aliases": [
"CVE-2026-89651"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-09-11T20:19:51Z",
"severity": "CRITICAL"
},
"details": "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.",
"id": "GHSA-vqxr-6xh4-gccq",
"modified": "2026-09-13T09:32:26Z",
"published": "2026-09-11T21:31:35Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-89651"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/5f892c767b30e4fb0c744c59f9235c717383d2cd"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/77933e22adfe813be2bd10be08d6e950103c3967"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/c37db86d2b5e9b57001ccae7e7a727e95a4f9c02"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dc5c7dffda92ef372fa587c444a1c537373df824"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
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