{"id":"CVE-2026-89541","aliases":[],"url":"https://o3.security/vulnerability/CVE-2026-89541","summary":"SUNRPC: harden gss_unwrap_resp_priv length checks","details":"In the Linux kernel, the following vulnerability has been resolved:\n\nSUNRPC: harden gss_unwrap_resp_priv length checks\n\ngss_unwrap_resp_priv() validates the RPCSEC_GSS opaque length with\n\n    offset = (u8 *)(p) - (u8 *)head->iov_base;\n    if (offset + opaque_len > rcv_buf->len)\n            goto unwrap_failed;\n    maj_stat = gss_unwrap(ctx->gc_gss_ctx, offset,\n                          offset + opaque_len, rcv_buf);\n\nBoth operands are u32 and the sum is computed in u32. A reply with\nopaque_len near 0xffffffff makes offset + opaque_len wrap to a small\nvalue that is below rcv_buf->len, so the bound check passes and\ngss_unwrap() is called with end < begin. The check also lacks a\nlower bound, so any opaque_len in [0, GSS_KRB5_TOK_HDR_LEN) is\naccepted and forwarded to gss_krb5_unwrap_v2(), whose pre-decrypt\nheader reads at ptr+4 and ptr+6 then run past the token.\n\nA krb5p NFS server returning a crafted RPCSEC_GSS reply can drive\nthe client into out-of-bounds reads in gss_krb5_unwrap_v2() and the\nrotate_left() loop that follows.\n\nFix by replacing the single combined check with three guards that\nare safe in u32 arithmetic and that enforce the RFC 4121 minimum\nouter token length:\n\n    if (offset > rcv_buf->len)\n            goto unwrap_failed;\n    if (opaque_len > rcv_buf->len - offset)\n            goto unwrap_failed;\n    if (opaque_len < GSS_KRB5_TOK_HDR_LEN)\n            goto unwrap_failed;\n\nThe first guard makes the subtraction in the second guard\nunconditionally safe; offset is derived from a successful\nxdr_inline_decode() in the head kvec, so in practice it already\nsatisfies the bound. The floor mirrors the server-side check added\nin commit 5b757c2e57a5 (\"SUNRPC: svcauth_gss: enforce krb5 token\nminimum length\").","published":"2026-09-11T19:44:18.188Z","modified":"2026-09-14T03:46:12.039741747Z","cvss":{"score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"Linux","name":"Kernel","fixedVersion":"6.12.109"}],"fix":null,"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/87831b92112c81db251d46756d65daa4f91af6a2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/89a15a50f84d32d4b99db86f957427fcbe20a99a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/d395c30d570ca6168f0297b191709927d1258273"},{"type":"WEB","url":"https://git.kernel.org/stable/c/ebcbd2523a8524c3d24e111cdbed8e271d910269"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/89xxx/CVE-2026-89541.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-89541"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-14T03:46:12.039741747Z"}}