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

• Severity: critical (CVSS 9.0 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 13.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2020-11-11 · updated 2026-06-17
• Weakness: CWE-863

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.

Affected products

• Microsoft Windows Server 2012: r2
• Microsoft Windows Server 2016: 20h2, 1903, 1909, 2004
• Microsoft Windows Server 2019: all versions
• Samba: from 4.1.0 before 4.13.13; from 4.14.0 before 4.14.9; from 4.15.0 before 4.15.1 — fixed in 4.13.13, 4.14.9, 4.15.1
• Microsoft Windows Server 2008 R2 Service Pack 1: from 6.1.0 before 6.1.7601.25661 — fixed in 6.1.7601.25661
• Microsoft Windows Server 2008 Service Pack 2: from 6.0.0 before 6.0.6003.21167 — fixed in 6.0.6003.21167
• Microsoft Windows Server 2012: from 6.2.0 before 6.2.9200.23409 — fixed in 6.2.9200.23409
• Microsoft Windows Server 2012 R2: from 6.3.0 before 6.3.9600.20069 — fixed in 6.3.9600.20069
• Microsoft Windows Server 2016: from 10.0.0 before 10.0.14393.4530 — fixed in 10.0.14393.4530
• Microsoft Windows Server 2019: from 10.0.0 before 10.0.17763.2061 — fixed in 10.0.17763.2061
• Microsoft Windows Server, version 1903 (Server Core installation): from 10.0.0 before publication — fixed in publication
• Microsoft Windows Server, version 1909 (Server Core installation): from 10.0.0 before publication — fixed in publication
• Microsoft Windows Server version 2004: from 10.0.0 before 10.0.19041.1110 — fixed in 10.0.19041.1110
• Microsoft Windows Server version 20H2: from 10.0.0 before 10.0.19041.1110 — fixed in 10.0.19041.1110

How to fix

Upgrade to a fixed version: Samba 4.13.13, 4.14.9, 4.15.1; Microsoft Windows Server 2008 R2 Service Pack 1 6.1.7601.25661; Microsoft Windows Server 2008 Service Pack 2 6.0.6003.21167; Microsoft Windows Server 2012 6.2.9200.23409; Microsoft Windows Server 2012 R2 6.3.9600.20069; Microsoft Windows Server 2016 10.0.14393.4530; Microsoft Windows Server 2019 10.0.17763.2061; Microsoft Windows Server, version 1903 (Server Core installation) publication; Microsoft Windows Server, version 1909 (Server Core installation) publication; Microsoft Windows Server version 2004 10.0.19041.1110; Microsoft Windows Server version 20H2 10.0.19041.1110. Check the vendor advisory for mitigations.

References

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

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