Medium [CVE-2025-3576] Krb5: kerberos rc4-hmac-md5 checksum vulnerability enabling message spoofing via md5 collisions

A vulnerability in the MIT Kerberos implementation allows GSSAPI-protected messages using RC4-HMAC-MD5 to be spoofed due to weaknesses in the MD5 checksum design. If RC4 is preferred over stronger encryption types, an attacker could exploit MD5 collisions to forge message integrity codes.

This may lead to unauthorized message tampering. This issue is classified as a moderate severity vulnerability because it affects the handling of PKINIT requests during ASN.1 decoding in krb5.

Exploitation requires specific and uncommon configurations, including a Kerberos environment with PKINIT enabled. Additionally, successful exploitation depends on triggering specific memory allocation failures or parser behaviors, contributing to a high attack complexity.

The attack requires that PKINIT is actively configured and in use, and cannot be exploited remotely without this setup in place, making the practical risk limited in standard environments. Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N).

Weakness: CWE-328.

Affected products named by the advisory: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 8.2 Advanced Update Support; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On; and 13 more.