---
id: CVE-2026-89537
title: |-
  In the Linux kernel, the following vulnerability has been resolved:

  SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2

  gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags
  byte at ptr[2], and padding at p…
summary: |-
  In the Linux kernel, the following vulnerability has been resolved:

  SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2

  gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags
  byte at ptr[2], and padding at p…
severity: critical
cvss: 9.1
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H'
cwe:
  - CWE-125
vendor: Linux
product: Linux
affected:
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    996dd15f60121bdd7896b4554458f8806d608063
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    7a946b2e7207f968902f2147ab9b30726f82f7ab
  - >-
    Linux >= de9c17eb4a912c9028f7b470eb80815144883b26 <
    b94f6719dcd9f7a609bc5f459f85795900e77d25
  - Linux 2.6.35
published: '2026-09-11'
updated: '2026-10-15'
sourceUpdated: '2026-10-15T11:17:54.090'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89537'
references:
  - url: 'https://git.kernel.org/stable/c/7a946b2e7207f968902f2147ab9b30726f82f7ab'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/996dd15f60121bdd7896b4554458f8806d608063'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: 'https://git.kernel.org/stable/c/b94f6719dcd9f7a609bc5f459f85795900e77d25'
    label: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89537.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-89537'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2532109'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-89537'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-89537'
  - url: >-
      https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-89537.mbox
  - url: 'https://git.kernel.org/stable/c/b2e9e10f5a536befcdce64d3e6946dff42fb823e'
  - url: 'https://git.kernel.org/stable/c/997577c52487181226775db3755079a3ba1d52b9'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
  - score-dispute
epss: 0.00653
epssPercentile: 0.51096
scores:
  nvd: 9.1
  cna: 9.1
  vendor: 7
ingestedAt: '2026-09-14T15:23:07.474Z'
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-16T19:23:15.980324Z'
---

## Overview

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

SUNRPC: Reject short RFC 4121 MIC tokens in gss_krb5_verify_mic_v2

gss_krb5_verify_mic_v2() reads the token ID at ptr[0..1], the flags
byte at ptr[2], and padding at ptr[3..7], then passes
ptr + GSS_KRB5_TOK_HDR_LEN and cksum_len to gss_krb5_mic_build_sg().
None of these accesses check read_token->len first.

The minimum safe token size is GSS_KRB5_TOK_HDR_LEN (16) plus
ctx->krb5e->cksum_len (12-24, depending on the enctype).  All callers
accept shorter tokens from the wire:

 - gss_unwrap_resp_integ() enforces only an upper bound
   (offset + len <= rcv_buf->len) before allocating
   mic.data = kmalloc(len) and passing it to gss_verify_mic().
   A malicious NFS server can therefore supply a short checksum
   opaque, producing a small slab allocation that the Kerberos MIC
   verifier reads past.

 - gss_validate() enforces only len <= RPC_MAX_AUTH_SIZE (400)
   before passing the wire-supplied length to
   gss_validate_seqno_mic(), which constructs a mic xdr_netobj
   and calls gss_verify_mic().

 - svcauth_gss_verify_header() enforces only
   checksum.len >= XDR_UNIT (4 bytes) before dispatching to
   gss_verify_mic().

 - svcauth_gss_unwrap_integ() checks only that the checksum fits
   in gsd->gsd_scratch.

Add a length guard at the top of gss_krb5_verify_mic_v2(), before any
ptr[] access or scatterlist construction.  Well-formed MIC tokens from
gss_krb5_get_mic_v2() already have exactly GSS_KRB5_TOK_HDR_LEN +
cksum_len bytes, so valid traffic is unaffected.

## Remediation

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

## Vendor advisories

- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, … · updated 2026-09-18 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-89537.json)