{"cve":"CVE-2026-89551","nvd":{"published":"2026-09-11T20:19:38.640","modified":"2026-10-19T09:17:50.393","status":"Received","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H","score":9.8},"cwes":[],"references":["https://git.kernel.org/stable/c/3f491306dcb673ff5e78e1044ba450c58978774e","https://git.kernel.org/stable/c/4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4","https://git.kernel.org/stable/c/85e9602650e9df07190abe817cee3b4d9bc3df17","https://git.kernel.org/stable/c/a3d77bcd974b8625d16bddf448cb3a1b5e37049c","https://git.kernel.org/stable/c/a924ac4c78afab71bf82641afa3b62e0c4a8b55e"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:53:43.293028046+00:00"},"epss":{"cve":"CVE-2026-89551","score":0.00514,"percentile":0.43521,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}