Is CVE-2026-40355 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-40355 being exploited in the wild.

How severe is CVE-2026-40355?

Medium severity, with a CVSS score of 5.9, published 28 April 2026.

Which products and versions are affected?

Mit Kerberos 5 1.18.0 to 1.22.2.

Is there a fix for CVE-2026-40355?

A patch was published on 2026-04-28: Upstream fix committed to krb5 repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-40355 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-40355?

Check whether you run Mit Kerberos 5 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-40355: MIT Kerberos 5 NULL pointer dereference in NegoEx parsing

CVE-2026-40355 · Severity: medium · CVSS 5.9 · Published 2026-04-28

MIT Kerberos 5 is a widely used authentication protocol that secures logins for millions of users and enterprise systems like Microsoft Active Directory. A vulnerability in its NegoEx parsing component allows an unauthenticated remote attacker to crash the authentication service by sending a specially crafted network packet. This results in a denial-of-service, preventing users from logging into affected systems and disrupting business operations.

Technologies: Mit Kerberos 5. Vendors: Mit.

Quick answers

Is CVE-2026-40355 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-40355 being exploited in the wild.
How severe is CVE-2026-40355?: Medium severity, with a CVSS score of 5.9, published 28 April 2026.
Which products and versions are affected?: Mit Kerberos 5 1.18.0 to 1.22.2.
Is there a fix for CVE-2026-40355?: A patch was published on 2026-04-28: Upstream fix committed to krb5 repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-40355 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-40355?: Check whether you run Mit Kerberos 5 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

A NULL pointer dereference exists in the NegoEx parsing logic of MIT Kerberos 5 (krb5). The vulnerability is located in the parse_nego_message() function within src/lib/gssapi/spnego/negoex_util.c, where the return value of a vector_base() call is dereferenced without a NULL check. An unauthenticated remote attacker can trigger this flaw by sending a crafted NegoEx message to an application calling gss_accept_sec_context() on a system where NegoEx is registered. This results in a process crash (DoS). The issue is fixed in version 1.22.3.

Affected products

MIT Kerberos 5 1.18.0 to 1.22.2

Timeline

2026-04-27: disclosed: Initial disclosure by researcher Cem Onat Karagun
2026-04-28: advisory: NVD and MITRE publish CVE-2026-40355
2026-04-28: patched: Upstream fix committed to krb5 repository

References

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