CVE-2026-20849: Microsoft Windows Kerberos privilege escalation via untrusted input

CVE-2026-20849 · Severity: high · CVSS 7.5 · Published 2026-01-13

A security vulnerability exists in Windows Kerberos, the primary system used for verifying user identities in corporate networks. An attacker who already has basic access to the network could exploit this flaw to gain higher-level administrative privileges. This could allow them to access sensitive data or perform unauthorized actions across the organization's infrastructure.

Technologies: Microsoft Windows 11, Microsoft Windows Server 2008 R2, Microsoft Windows 10. Vendors: Microsoft.

Quick answers

Is CVE-2026-20849 exploited in the wild?
No. Junglewise Threat Intelligence has no report of CVE-2026-20849 being exploited in the wild.
How severe is CVE-2026-20849?
High severity, with a CVSS score of 7.5, published 13 January 2026.
Which products and versions are affected?
Microsoft Windows 11 22H3, 23H2, 24H2, 25H2; Microsoft Windows Server 2008 R2 All versions; Microsoft Windows 10 1607, 1809, 21H2, 22H2.
Is there a fix for CVE-2026-20849?
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-2026-20849 attacked?
It is attacked over the network, in an operating system.
Am I affected by CVE-2026-20849?
Check whether you run Microsoft Windows 11, Microsoft Windows Server 2008 R2 or Microsoft Windows 10 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 privilege escalation vulnerability exists in the Windows Kerberos authentication protocol due to a reliance on untrusted inputs in a security decision (CWE-807). An authenticated attacker with low privileges can exploit this over the network by providing specially crafted input that influences security-critical decisions within the Kerberos service. Successful exploitation requires the attacker to overcome high complexity conditions, but it can result in a complete compromise of confidentiality, integrity, and availability. Microsoft has released security updates to address this issue across affected Windows and Windows Server versions.

Affected products

  • Microsoft Windows 10 1607, 1809, 21H2, 22H2
  • Microsoft Windows 11 22H3, 23H2, 24H2, 25H2
  • Microsoft Windows Server 2008 R2 Service Pack 1 All versions

Timeline

  • 2026-01-13: disclosed
  • 2026-01-13: advisory

References

This page as Markdown. Free to reuse under CC BY 4.0 with a link back.