Skip to main content
cve.nowby Sazabi
← All vulnerabilities
CVE-2026-89551

SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
None on Exploit-DB, Metasploit or GitHub
  • Exploitation: none
  • Automatable: yes
  • Technical impact: total

Summary

In the Linux kernel, the following vulnerability has been resolved: SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow xdr_buf_trim() trims `len` bytes from the tail of an xdr_buf by walking the tail, pages, and head iovecs. Each per-section step uses min_t() so it never removes more bytes than that section holds, but the final accounting at the fix_len label subtracts the total bytes actually consumed from buf->len without any clamp: fix_len: buf->len -= (len - trim); When the caller has set buf->len to a value smaller than the sum of the iov_lens, (len - trim) can exceed buf->len and the unsigned subtraction wraps to near UINT_MAX. gss_krb5_unwrap_v2() reaches xdr_buf_trim() in exactly that state: buf->head[0].iov_len -= GSS_KRB5_TOK_HDR_LEN + headskip; buf->len = len - (GSS_KRB5_TOK_HDR_LEN + headskip); xdr_buf_trim(buf, ec + GSS_KRB5_TOK_HDR_LEN + tailskip); buf->len is a small wire-derived value while the iov_lens are at page scale, so the per-section loops legitimately consume far more bytes than buf->len records. The wrapped buf->len then propagates as the authoritative stream bound into every downstream XDR decoder. Fix by clamping the decrement so buf->len bottoms out at zero: buf->len -= min_t(unsigned int, buf->len, len - trim); On the normal path where the iov_lens sum to buf->len, (len - trim) is always <= buf->len and the result is identical to before. No callers change behavior outside the underflow case.

Timeline

  1. CVE published
  2. CISA SSVC assessment

    Exploitation: none · Automatable: yes · Technical impact: total

  3. Record last updated

Affected versions

  • Linux Linux

    From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in a3d77bcd974b8625d16bddf448cb3a1b5e37049c; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in fa16bbe987b47e771e52eeb1b4540f18d92496ac; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in a924ac4c78afab71bf82641afa3b62e0c4a8b55e; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in 4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in e6267cccd7b05cc514e57f2160aa8db85f5c2701; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in ad0cce80d4af2f74674e8b635d97aa3880e83da8; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in 85e9602650e9df07190abe817cee3b4d9bc3df17; From 4c190e2f913f038c9c91ee63b59cd037260ba353 · fixed in 3f491306dcb673ff5e78e1044ba450c58978774e

  • Linux Linux

    3.9

  • KernelLinux

    From 3.9.0 · fixed in 5.10.270; From 5.11.0 · fixed in 5.15.221; From 5.16.0 · fixed in 6.1.188; From 6.2.0 · fixed in 6.6.157; From 6.7.0 · fixed in 6.12.109; From 6.13.0 · fixed in 6.18.50; From 6.19.0 · fixed in 7.2.4

References 8

git.kernel.org