CVE-2025-29809: 
vulnerability analysis and mitigation

A security feature bypass vulnerability exists in Windows Kerberos that allows an authorized attacker to bypass credential protection mechanisms locally. The vulnerability (CVE-2025-29809) was discovered and disclosed in April 2025, affecting Windows systems with Credential Guard enabled. This vulnerability received a CVSS v3.1 base score of 7.1 (HIGH) (NVD).

The vulnerability stems from insufficient validation of the Kerberos krbtgt service name within the TGT (Ticket Granting Ticket). The issue specifically relates to how Kerberos handles canonicalization of principal names and the validation performed by the KerbGetFlagsForKdcReply function within the KerbClientShared.dll. The vulnerability allows bypassing Credential Guard protections through manipulation of the service name format, particularly using X500 (LDAP distinguished name) formatting (NetSPI Blog).

When successfully exploited, this vulnerability allows an authorized attacker to bypass Microsoft's Credential Guard protection and extract Kerberos Ticket Granting Tickets (TGTs) that should otherwise be protected. This could potentially lead to unauthorized access to sensitive credential information that Credential Guard is designed to protect (NetSPI Blog).

Microsoft has released patches for this vulnerability as part of the April 2025 Patch Tuesday updates. The fix includes updates to the KerbGetFlagsForKdcReply function to properly check for X500 formatting of the krbtgt principal name and normalize distinguished names to prevent character escaping bypasses. Organizations are strongly advised to apply these security updates to prevent exploitation (ZDI).