{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-89551", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-11T19:38:34.723Z", "datePublished": "2026-09-11T19:44:25.327Z", "dateUpdated": "2026-10-19T08:48:44.059Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T08:48:44.059Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow\n\nxdr_buf_trim() trims `len` bytes from the tail of an xdr_buf by\nwalking the tail, pages, and head iovecs. Each per-section step\nuses min_t() so it never removes more bytes than that section\nholds, but the final accounting at the fix_len label subtracts the\ntotal bytes actually consumed from buf->len without any clamp:\n\n fix_len:\n buf->len -= (len - trim);\n\nWhen the caller has set buf->len to a value smaller than the sum\nof the iov_lens, (len - trim) can exceed buf->len and the unsigned\nsubtraction wraps to near UINT_MAX. gss_krb5_unwrap_v2() reaches\nxdr_buf_trim() in exactly that state:\n\n buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip;\n buf->len = len - (GSS_KRB5_TOK_HDR_LEN + headskip);\n xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip);\n\nbuf->len is a small wire-derived value while the iov_lens are at\npage scale, so the per-section loops legitimately consume far more\nbytes than buf->len records. The wrapped buf->len then propagates\nas the authoritative stream bound into every downstream XDR\ndecoder.\n\nFix by clamping the decrement so buf->len bottoms out at zero:\n\n buf->len -= min_t(unsigned int, buf->len, len - trim);\n\nOn the normal path where the iov_lens sum to buf->len, (len - trim)\nis always <= buf->len and the result is identical to before. No\ncallers change behavior outside the underflow case." } ], "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 - xdr_buf_trim() is reached from nfsd RPCSEC_GSS privacy unwrap on TCP/2049 (svcauth_gss_unwrap_priv → gss_unwrap → gss_krb5_unwrap_v2) and from the NFS client's gss_unwrap_resp_priv() on every krb5p reply, so a remote NFS peer delivers the wrap token over the network.\nAC:L - A peer holding the GSS session keys can encrypt a RFC 4121 wrap token so that after decrypt, buf->len is a small wire-derived value while iov_lens remain page-scale; xdr_buf_trim() then subtracts more than buf->len and wraps, with no race or layout outside attacker control.\nPR:N - A malicious or compromised NFS server that already shares a krb5p GSS context needs no account or capability on the victim client; ordinary krb5p replies and NFSv4.0 GSS callbacks are processed without local privileges on that host.\nUI:N - Once a krb5p NFS mount exists, the client unwraps every privacy-protected reply and NFSv4.0 GSS callback with no further mount, click, or open; idle revalidations and server-driven callbacks are sufficient.\nS:U - The wrapped buf->len and subsequent XDR decode run in the host kernel that processed the RPC and do not cross a VM, IOMMU, or sandbox boundary.\nC:H - The underflowed buf->len (~UINT_MAX) becomes the authoritative stream bound, and on nfsd xdr->nwords also underflows via saved_len - buf->len, so later xdr_read_pages/xdr_shrink_bufhead and NFS XDR decoders read far past the receive buffer into adjacent kernel memory.\nI:H - xdr_shrink_bufhead() calls xdr_buf_head_shift_right() with a near-UINT_MAX length derived from the wrapped buf->len, and garbage xdr_stream_pos values can index the svc pages[] array out of bounds, an out-of-bounds write exploitable for control-flow hijacking.\nA:H - Those unbounded XDR copies and the inconsistent xdr_buf (wrapped length versus iov_lens) oops or panic nfsd or the NFS client, and the peer can repeat the request at will." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/sunrpc/xdr.c" ], "versions": [ { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "a3d77bcd974b8625d16bddf448cb3a1b5e37049c", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "fa16bbe987b47e771e52eeb1b4540f18d92496ac", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "a924ac4c78afab71bf82641afa3b62e0c4a8b55e", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "e6267cccd7b05cc514e57f2160aa8db85f5c2701", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "ad0cce80d4af2f74674e8b635d97aa3880e83da8", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "85e9602650e9df07190abe817cee3b4d9bc3df17", "status": "affected", "versionType": "git" }, { "version": "4c190e2f913f038c9c91ee63b59cd037260ba353", "lessThan": "3f491306dcb673ff5e78e1044ba450c58978774e", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/sunrpc/xdr.c" ], "versions": [ { "version": "3.9", "status": "affected" }, { "version": "0", "lessThan": "3.9", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.270", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.221", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.188", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.157", "lessThanOrEqual": "6.6.*", "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": "3.9", "versionEndExcluding": "5.10.270" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "5.15.221" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "6.1.188" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "6.6.157" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "6.12.109" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "6.18.50" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "7.2.4" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.9", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/a3d77bcd974b8625d16bddf448cb3a1b5e37049c" }, { "url": "https://git.kernel.org/stable/c/fa16bbe987b47e771e52eeb1b4540f18d92496ac" }, { "url": "https://git.kernel.org/stable/c/a924ac4c78afab71bf82641afa3b62e0c4a8b55e" }, { "url": "https://git.kernel.org/stable/c/4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4" }, { "url": "https://git.kernel.org/stable/c/e6267cccd7b05cc514e57f2160aa8db85f5c2701" }, { "url": "https://git.kernel.org/stable/c/ad0cce80d4af2f74674e8b635d97aa3880e83da8" }, { "url": "https://git.kernel.org/stable/c/85e9602650e9df07190abe817cee3b4d9bc3df17" }, { "url": "https://git.kernel.org/stable/c/3f491306dcb673ff5e78e1044ba450c58978774e" } ], "title": "SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow", "x_generator": { "engine": "bippy-1.2.0" } }, "adp": [ { "metrics": [ { "other": { "type": "ssvc", "content": { "id": "CVE-2026-89551", "role": "CISA Coordinator", "options": [ { "Exploitation": "none" }, { "Automatable": "yes" }, { "Technical Impact": "total" } ], "version": "2.0.3", "timestamp": "2026-10-16T19:23:51.789342Z" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-10-16T19:26:43.285Z" } } ] } }