CVE-2026-89551: SUNRPC: xdr_buf_trim: clamp buf->len to avoid underflow
- Is it exploited?
Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of . If CISA adds it, this page shows it as known exploited.
- How likely is exploitation in the next 30 days?
- 0.5%
EPSS score, percentile 43.7 of all scored records. A probability estimated by FIRST, not a report of exploitation.
- How severe?
- 9.8 Critical
CVSS v3.1 base score, given by the CNA
- What should I do?
CISA has set no required action, because the vulnerability is not in KEV.
The CVE record links no vendor advisory, patch or mitigation.
- Which versions are affected?
Affected
- 3.9
Unaffected before 3.9; 5.10.270; 5.15.221; 6.1.188; 6.6.157; 6.12.109; and 3 more
Source: CISA KEV 2026.10.29, as of ; FIRST EPSS, as of ; CVE List, as of . About the data.
What to do
Advisories and patches
The CVE record links no vendor advisory, patch or mitigation.
This summary is based on the CVE record as of . Check the vendor's advisory before you act: affected versions and fixes can change.
Affected products and versions
As listed in the CVE record.
| Status | Versions |
|---|---|
| Affected | from 4c190e2f913f to before a3d77bcd974b |
| Affected | from 4c190e2f913f to before fa16bbe987b4 |
| Affected | from 4c190e2f913f to before a924ac4c78af |
| Affected | from 4c190e2f913f to before 4bf59cb0ea5b |
| Affected | from 4c190e2f913f to before e6267cccd7b0 |
| Affected | from 4c190e2f913f to before ad0cce80d4af |
| Affected | from 4c190e2f913f to before 85e9602650e9 |
| Affected | from 4c190e2f913f to before 3f491306dcb6 |
Versions not listed are: unaffected.
| Status | Versions |
|---|---|
| Affected | 3.9 |
| Unaffected | before 3.9 |
| Unaffected | 5.10.270 |
| Unaffected | 5.15.221 |
| Unaffected | 6.1.188 |
| Unaffected | 6.6.157 |
| Unaffected | 6.12.109 |
| Unaffected | 6.18.50 |
| Unaffected | 7.2.4 |
| Unaffected | 7.3 |
Versions not listed are: affected.
Versions the record lists as unaffected: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50, 7.2.4, 7.3.
Source: CVE List, as of . About the data.
About this vulnerability
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 act…
Summary: CVE record, as of .
- CISA has not added CVE-2026-89551 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
- The CVE record was published on 11 Sep 2026.
- The CVE record carries a CVSS v3.1 base score of 9.8 (Critical), given by its CNA.
- FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.5% (percentile 43.7), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
- CISA's SSVC assessment in the CVE record: exploitation none, automatable yes, technical impact total.
Source: CISA KEV 2026.10.29, as of ; CVE List, as of ; FIRST EPSS, as of . About the data.
Description
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.
Source: CVE List, as of . About the data.
Timeline
| Date | Event |
|---|---|
| CVE record published | |
| CVE record last updated |
References
8
Known exploited Linux vulnerabilities
- CVE-2026-46300: Linux Kernel Missing Initialization of a Variable Vulnerability
- CVE-2025-39682: Linux Kernel Improper Check for Unusual or Exceptional Conditions Vulnerability
- CVE-2025-39964: Linux Kernel Race Condition Vulnerability
- CVE-2026-53266: Linux Kernel Out-of-Bounds Write Vulnerability
- CVE-2026-53362: Linux Kernel Unspecified Vulnerability