SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow
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.
CVE-2026-89551
Primary source · Revision 1
Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.
Security context
Source reference: cve:CVE-2026-89551
Linux
Source reference: /containers/cna/affected/0/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Linux
Source reference: /containers/cna/affected/1/product
- Affected versions
- Not stated in this record
- Fixed versions
- Not stated in this record
- Prerequisites
- Not stated in this record
Structured affected-version data
Original package identities and version rules from this source.
[
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "a3d77bcd974b8625d16bddf448cb3a1b5e37049c",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "fa16bbe987b47e771e52eeb1b4540f18d92496ac",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "a924ac4c78afab71bf82641afa3b62e0c4a8b55e",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "4bf59cb0ea5b0ddfbc46a1dc2fa78fc8b9986ce4",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "e6267cccd7b05cc514e57f2160aa8db85f5c2701",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "ad0cce80d4af2f74674e8b635d97aa3880e83da8",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "85e9602650e9df07190abe817cee3b4d9bc3df17",
"versionType": "git"
},
{
"status": "affected",
"version": "4c190e2f913f038c9c91ee63b59cd037260ba353",
"lessThan": "3f491306dcb673ff5e78e1044ba450c58978774e",
"versionType": "git"
}
],
"programFiles": [
"net/sunrpc/xdr.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "3.9"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "3.9",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.270",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.221",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.188",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.157",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.109",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.50",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.4",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"net/sunrpc/xdr.c"
],
"defaultStatus": "affected"
}
]- Related CVEs
- CVE-2026-89551
Source reference:
/cveMetadata/cveId
Publisher severity
critical
Source reference: /containers/cna/metrics
- Event
- #35067 · Revision 1
- Added to Heist Feed
- Publisher date