---
id: CVE-2026-89550
title: 'SUNRPC: svcauth_gss: enforce krb5 token minimum length'
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  SUNRPC: svcauth_gss: enforce krb5 token minimum length

  svcauth_gss_unwrap_priv() validates only an upper bound on the
  wire-supplied opaque length before handing the bu…
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 >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c <
    0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd
  - >-
    Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c <
    dd6afc6cab8c5d387d1ed2f069562ef7bdadd651
  - >-
    Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c <
    de942dd8c2c8358bcad04ce44271954c48924423
  - >-
    Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c <
    2eed1e6a976a44015c3ee78841fe336796e2b21c
  - >-
    Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c <
    a919c5c88769cf8fb3ec071e6078d830bf512489
  - Linux 2.6.18
published: '2026-09-11'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T12:00:53.633Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-89550'
references:
  - url: 'https://git.kernel.org/stable/c/0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd'
  - url: 'https://git.kernel.org/stable/c/dd6afc6cab8c5d387d1ed2f069562ef7bdadd651'
  - url: 'https://git.kernel.org/stable/c/de942dd8c2c8358bcad04ce44271954c48924423'
  - url: 'https://git.kernel.org/stable/c/2eed1e6a976a44015c3ee78841fe336796e2b21c'
  - url: 'https://git.kernel.org/stable/c/a919c5c88769cf8fb3ec071e6078d830bf512489'
tags:
  - cve.org
epss: 0.00671
epssPercentile: 0.49864
ingestedAt: '2026-09-14T15:23:07.452Z'
---

## Overview

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

SUNRPC: svcauth_gss: enforce krb5 token minimum length

svcauth_gss_unwrap_priv() validates only an upper bound on the
wire-supplied opaque length before handing the buffer to
gss_unwrap():

    if (len > xdr_stream_remaining(xdr))
            goto unwrap_failed;
    offset = xdr_stream_pos(xdr);
    ...
    maj_stat = gss_unwrap(ctx, offset, offset + len, buf);

The wire value `len` flows unchanged as the upper bound into the
krb5 unwrap path, so a len in [0, 16] passes this check and is
handed to gss_unwrap(). For a krb5 v2 context that lands in
gss_krb5_unwrap_v2(), which reads the 16-byte RFC 4121 token
header fields at ptr+4 and ptr+6 and then calls rotate_left()
before any integrity check. With a sub-header length the header
reads run past the token, and _rotate_left()'s `shift %= buf->len`
path can divide by zero when buf->len has been driven to zero by
the truncated token. A header-only token (len == 16) is equally
invalid: with a non-zero RRC field and the opaque blob ending at
the XDR buffer boundary, rotate_left() builds a zero-length
subbuffer, reaching the same division.

Reject the token at the server entry point before it reaches the
krb5 unwrap core. A valid sealed RFC 4121 token must contain
the 16-byte header plus at least some encrypted payload.

Fix by adding a minimum-length check immediately after the
existing upper-bound check:

    if (len <= GSS_KRB5_TOK_HDR_LEN)
            goto unwrap_failed;

## Affected

- `Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c < 0ea5b0c7f212c2772d32c2b88287b89a9cdf6edd`
- `Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c < dd6afc6cab8c5d387d1ed2f069562ef7bdadd651`
- `Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c < de942dd8c2c8358bcad04ce44271954c48924423`
- `Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c < 2eed1e6a976a44015c3ee78841fe336796e2b21c`
- `Linux >= 7c9fdcfb1b64c47ed618c103b617af3f86e1239c < a919c5c88769cf8fb3ec071e6078d830bf512489`
- `Linux 2.6.18`

## Remediation

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