{"id":"CVE-2026-89551","title":"SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow","summary":"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…","severity":"critical","cvss":9.8,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","cwe":["CWE-191"],"vendor":"Linux","product":"Linux","affected":["Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < a3d77bcd974b8625d16bddf448cb3a1b5e37049c","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < fa16bbe987b47e771e52eeb1b4540f18d92496ac","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < a924ac4c78afab71bf82641afa3b62e0c4a8b55e","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < e6267cccd7b05cc514e57f2160aa8db85f5c2701","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < ad0cce80d4af2f74674e8b635d97aa3880e83da8","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 85e9602650e9df07190abe817cee3b4d9bc3df17","Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 3f491306dcb673ff5e78e1044ba450c58978774e","Linux 3.9"],"ssvc":{"exploitation":"none","automatable":"yes","technicalImpact":"total","timestamp":"2026-10-16T19:23:51.789342Z"},"published":"2026-09-11","updated":"2026-10-19","sourceUpdated":"2026-10-19T08:48:44.059Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-89551","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"},{"url":"https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89551.json"},{"url":"https://access.redhat.com/security/cve/CVE-2026-89551"},{"url":"https://bugzilla.redhat.com/show_bug.cgi?id=2532375"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-89551"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89551"},{"url":"https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89551.mbox"}],"tags":["cve.org","csaf","vex","red-hat","score-dispute"],"epss":0.00514,"epssPercentile":0.43607,"scores":{"cna":9.8,"vendor":7},"ingestedAt":"2026-09-14T15:23:07.452Z","slug":"CVE-2026-89551","body":"## Overview\n\nIn 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.\n\n## Affected\n\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < a3d77bcd974b8625d16bddf448cb3a1b5e37049c`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < fa16bbe987b47e771e52eeb1b4540f18d92496ac`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < a924ac4c78afab71bf82641afa3b62e0c4a8b55e`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < e6267cccd7b05cc514e57f2160aa8db85f5c2701`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < ad0cce80d4af2f74674e8b635d97aa3880e83da8`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 85e9602650e9df07190abe817cee3b4d9bc3df17`\n- `Linux >= 4c190e2f913f038c9c91ee63b59cd037260ba353 < 3f491306dcb673ff5e78e1044ba450c58978774e`\n- `Linux 3.9`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Vendor advisories\n\n- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-09-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89551.json)","depth":"midnight","depthScore":54,"depthScoreParts":{"impact":53.9,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[{"seq":223287,"id":"CVE-2026-89551","ts":1792180044372,"field":"cvss","old":"7","new":"9.8"},{"seq":223286,"id":"CVE-2026-89551","ts":1792180044372,"field":"severity","old":"high","new":"critical"},{"seq":205440,"id":"CVE-2026-89551","ts":1789576714072,"field":"cvss","old":"9.8","new":"7"},{"seq":205439,"id":"CVE-2026-89551","ts":1789576714072,"field":"severity","old":"critical","new":"high"},{"seq":197935,"id":"CVE-2026-89551","ts":1789384321031,"field":"cvss","old":"7.4","new":"9.8"},{"seq":197934,"id":"CVE-2026-89551","ts":1789384321031,"field":"severity","old":"high","new":"critical"},{"seq":183744,"id":"CVE-2026-89551","ts":1789356677206,"field":"cvss","old":"9.8","new":"7.4"},{"seq":183743,"id":"CVE-2026-89551","ts":1789356677206,"field":"severity","old":"critical","new":"high"},{"seq":153358,"id":"CVE-2026-89551","ts":1789285350188,"field":"cvss","old":null,"new":"9.8"},{"seq":153357,"id":"CVE-2026-89551","ts":1789285350188,"field":"severity","old":"none","new":"critical"},{"seq":147323,"id":"CVE-2026-89551","ts":1789270209730,"field":"cvss","old":null,"new":"7.4"},{"seq":147322,"id":"CVE-2026-89551","ts":1789270209730,"field":"severity","old":"none","new":"high"},{"seq":109076,"id":"CVE-2026-89551","ts":1789183730213,"field":"cvss","old":null,"new":"7.4"},{"seq":109075,"id":"CVE-2026-89551","ts":1789183730213,"field":"severity","old":"none","new":"high"}]}