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🛡️ CVE-2026-40356 — kerberos-5

🟡 CVSS 5.9 — Medium ⚠️ Exploit Public CWE-191 NVD
5.9
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

In MIT Kerberos 5 (aka krb5) before 1.22.3, there is an integer underflow and resultant out-of-bounds read if an application calls gss_accept_sec_context() on a system with a NegoEx mechanism registered in /etc/gss/mech. An unauthenticated remote attacker can trigger this, possibly causing the process to terminate in parse_message.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: High — the attacker first has to win a race, learn a secret or otherwise prepare the target.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-40356 is classified as CWE-191: Integer Underflow. A subtraction drops below the minimum for the type and wraps, yielding an unexpectedly large value.

Affected software

CVE-2026-40356 is recorded against 1 package.

  • kerberos-5 (from 1.18.0 up to 1.22.2)

Timeline and source

Published on 28 April 2026 and last revised on 8 July 2026. A public exploit is known to exist, which raises the urgency of patching considerably. A vendor advisory or fix has been published. Record sourced from NVD.

References

cems.fun
github.com
web.mit.edu

Other advisories for this package

kerberos-5 has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-191: Integer Underflow) in other software:

Details

Severity MEDIUM
CVSS Score 5.9
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE CWE-191
Public Exploit ⚠️ Yes
Source NVD
Published 2026-04-28
Updated 2026-08-20
Modified 2026-07-08

Affected Packages

Software From version Fixed in
kerberos-5 1.18.0 1.22.2

Similar Threats

Exploit Protection

Are you running kerberos-5?

CVE-2026-40356 carries CVSS 5.9 Medium rating and a public exploit already exists. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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