---
id: CVE-2026-89542
title: 'SUNRPC: harden gss_krb5_unwrap_v2 against short tokens'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  SUNRPC: harden gss_krb5_unwrap_v2 against short tokens

  gss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and
  ptr+6 before validating that the token is a…
severity: critical
cvss: 9.8
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H'
cvssSource: cna
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    299d281c7225ded15b28cb861a98d818d82787fc
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    84ddbc8d084c0251d534f14f5d1a7da05be56404
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    075d7cfc4df8c54cb202ba8b28420370c03ba9b6
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    f2591660e0eb263c9415bf0d0bb1b111e62df7a4
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    dddcb0f4b7e27fac16a78ea9a1c8ec2e8a241087
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    806584a4b67a7233870c33e5b8f872e76dd02988
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    a7894e10572d53eb10109b8d07459cc8d3435811
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    6959297aaa9572783d620a226d73c3fb94494888
  - Linux 2.6.35
published: '2026-09-11'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T12:00:49.355Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89542'
references:
  - url: 'https://git.kernel.org/stable/c/299d281c7225ded15b28cb861a98d818d82787fc'
  - url: 'https://git.kernel.org/stable/c/84ddbc8d084c0251d534f14f5d1a7da05be56404'
  - url: 'https://git.kernel.org/stable/c/075d7cfc4df8c54cb202ba8b28420370c03ba9b6'
  - url: 'https://git.kernel.org/stable/c/f2591660e0eb263c9415bf0d0bb1b111e62df7a4'
  - url: 'https://git.kernel.org/stable/c/dddcb0f4b7e27fac16a78ea9a1c8ec2e8a241087'
  - url: 'https://git.kernel.org/stable/c/806584a4b67a7233870c33e5b8f872e76dd02988'
  - url: 'https://git.kernel.org/stable/c/a7894e10572d53eb10109b8d07459cc8d3435811'
  - url: 'https://git.kernel.org/stable/c/6959297aaa9572783d620a226d73c3fb94494888'
tags:
  - cve.org
epss: 0.00755
epssPercentile: 0.53185
ingestedAt: '2026-09-14T15:23:07.452Z'
---

## Overview

In the Linux kernel, the following vulnerability has been resolved:

SUNRPC: harden gss_krb5_unwrap_v2 against short tokens

gss_krb5_unwrap_v2() reads the EC and RRC header fields at ptr+4 and
ptr+6 before validating that the token is at least GSS_KRB5_TOK_HDR_LEN
(16) bytes long, and its rotate_left() helper passes buf->len - base
to xdr_buf_subsegment() without verifying that base <= buf->len. When
a caller hands in a sub-16-byte token, or a token whose declared len
leaves base past the end of the buffer, three distinct failures follow:

    gss_krb5_unwrap_v2(offset, len, buf)
      ptr = buf->head[0].iov_base + offset
      ec  = *(ptr + 4)              /* OOB read on short head */
      rrc = *(ptr + 6)              /* OOB read on short head */
      rotate_left(offset + 16, buf, rrc)
        xdr_buf_subsegment(buf, &subbuf,
                           base, buf->len - base)   /* u32 wrap when base > len */
        _rotate_left(&subbuf, shift)
          shift %= buf->len         /* divide-by-zero when base == len */

After decryption, the cleanup arithmetic has the same shape:

    movelen = min_t(unsigned int, buf->head[0].iov_len, len);
    movelen -= offset + GSS_KRB5_TOK_HDR_LEN + headskip;
    BUG_ON(offset + GSS_KRB5_TOK_HDR_LEN + headskip + movelen >
                                            buf->head[0].iov_len);

The BUG_ON re-adds the value just subtracted, so it reduces to
min(A, B) > A and is permanently false; it cannot catch the unsigned
underflow of movelen, which then drives a ~UINT_MAX-byte memmove().

Add four defense-in-depth guards inside the unwrap core so it is safe
regardless of what its callers validate:

  - reject tokens with len - offset < GSS_KRB5_TOK_HDR_LEN before
    touching ptr+4/ptr+6;
  - bail from rotate_left() when buf->len <= base, covering both the
    underflow and zero-length cases;
  - return early from _rotate_left() when buf->len is zero, so the
    shift %= buf->len modulo cannot fault;
  - replace the dead BUG_ON with a live check that returns
    GSS_S_DEFECTIVE_TOKEN before the movelen subtraction.

## Affected

- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < 299d281c7225ded15b28cb861a98d818d82787fc`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < 84ddbc8d084c0251d534f14f5d1a7da05be56404`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < 075d7cfc4df8c54cb202ba8b28420370c03ba9b6`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < f2591660e0eb263c9415bf0d0bb1b111e62df7a4`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < dddcb0f4b7e27fac16a78ea9a1c8ec2e8a241087`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < 806584a4b67a7233870c33e5b8f872e76dd02988`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < a7894e10572d53eb10109b8d07459cc8d3435811`
- `Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 < 6959297aaa9572783d620a226d73c3fb94494888`
- `Linux 2.6.35`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.