SignXML's signature verification with HMAC is vulnerable to a timing attack
Date: 2025-06
Affected: pip/signxml
Attack vector: other
Category: vulnerability-disclosure
Severity: Medium
CVE: CVE-2025-48995
CWE: CWE-208

When verifying signatures with X509 certificate validation turned off and HMAC shared secret set (`signxml.XMLVerifier.verify(require_x509=False, hmac_key=...`), prior versions of SignXML are vulnerable to a potential timing attack. The verifier may leak information about the correct HMAC when comparing it with the user supplied hash, allowing users to reconstruct the correct HMAC for any data.


Mitigations:

Architectural layers (MAESTRO):