CVE-2025-3576: 
Kerberos vulnerability analysis and mitigation

A vulnerability in the MIT Kerberos implementation (CVE-2025-3576) allows GSSAPI-protected messages using RC4-HMAC-MD5 to be spoofed due to weaknesses in the MD5 checksum design. The vulnerability was discovered and disclosed on April 15, 2025, affecting MIT Kerberos implementations that use RC4-HMAC-MD5 encryption (NVD, Debian Tracker).

The vulnerability exists in the implementation of RC4-HMAC-MD5 checksums for GSSAPI-protected messages. If RC4 is preferred over stronger encryption types, an attacker could exploit MD5 collisions to forge message integrity codes. The vulnerability has been assigned a CVSS v3.1 Base Score of 5.9 (MEDIUM) with the vector string CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N, indicating network accessibility with high attack complexity and potential for high impact on integrity (NVD).

The vulnerability can lead to unauthorized message tampering in GSSAPI-protected communications. When exploited, attackers can spoof messages by crafting altered content that maintains the same Message Integrity Code (MIC), potentially compromising the integrity of authenticated communications (Red Hat Bugzilla).

The vulnerability requires specific conditions to be exploitable: the system must be using RC4-HMAC-MD5 for GSSAPI-protected communications, and the attacker must have network access to intercept and modify traffic. The attack relies on RC4 being chosen over stronger encryption options and requires attacker access to the network traffic (Red Hat Bugzilla).

Since MIT Kerberos 1.21, the KDC will no longer issue tickets with RC4 or triple-DES session keys unless explicitly configured with the new allow_rc4 or allow_des3 variables. Organizations should upgrade to the latest version and avoid using RC4-HMAC-MD5 encryption in favor of stronger alternatives (Debian Tracker).