# CVE-2026-42903: Microsoft Windows Kerberos null pointer dereference denial of service

Source: https://junglewise.ai/threats/cve-2026-42903-microsoft-windows-kerberos-null-pointer-dereference-denial-of  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-09. Updated: 2026-06-09  
License: CC BY 4.0 with a link back

CVE-2026-42903 · Severity: medium · CVSS 6.5 · Published 2026-06-09

A vulnerability exists in the Windows Kerberos authentication service, which is used to verify user identities across a network. An authorized user could exploit this flaw to crash the service, leading to a denial of service. This could disrupt login processes and access to corporate resources, impacting business operations and availability.

Technologies: [Microsoft Windows Kerberos](https://junglewise.ai/threats/technologies/windows-kerberos). Vendors: [Microsoft](https://junglewise.ai/threats/vendors/microsoft).

## Quick answers

**Is CVE-2026-42903 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42903 being exploited in the wild.

**How severe is CVE-2026-42903?** Medium severity, with a CVSS score of 6.5, published 9 June 2026.

**Which products and versions are affected?** Microsoft Windows Kerberos.

**Is there a fix for CVE-2026-42903?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-42903 attacked?** It is attacked over the network, in an operating system.

**Am I affected by CVE-2026-42903?** Check whether you run Microsoft Windows Kerberos. 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 vulnerability (CWE-476) exists within the Microsoft Windows Kerberos implementation. The flaw is triggered when the service improperly handles specific malformed requests, leading to a process crash. An attacker must be authenticated (Low Privileges) to reach the vulnerable code path over the network. Successful exploitation results in a denial of service (DoS) of the Kerberos authentication functionality, though it does not allow for information disclosure or remote code execution. Microsoft has released security updates to address this issue.

## Affected products

- Microsoft Windows Kerberos

## Timeline

- 2026-06-09: disclosed
- 2026-06-09: advisory

## References

- [https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42903](https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-42903)

## Related threats

- [Windows Kerberos use-after-free privilege escalation](https://junglewise.ai/threats/cve-2026-70241-use-after-free-in-windows-kerberos-allows-an-authorized-attacker)
- [Microsoft Windows Kerberos authentication bypass](https://junglewise.ai/threats/cve-2026-69676-microsoft-windows-kerberos-authentication-bypass)
- [Microsoft Windows Kerberos integer overflow remote code execution](https://junglewise.ai/threats/cve-2026-47288-microsoft-windows-kerberos-integer-overflow-remote-code-execution)