GHSA-gmhf-gg8w-jw42

SignXML's signature verification with HMAC is vulnerable to a timing attack

Source: GitHub Advisory Database (reviewed) Moderate CVE-2025-48995

Packages

Ecosystem	Package	Affected	Fixed in
PyPI	signxml	< 4.0.4	4.0.4

Details

As written in the advisory (Markdown source, shown as plain text).

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.

References

External links from the advisory. They lead to third-party sites.

https://github.com/XML-Security/signxml/security/advisories/GHSA-gmhf-gg8w-jw42 web
https://nvd.nist.gov/vuln/detail/CVE-2025-48995 advisory
https://github.com/XML-Security/signxml/commit/1b501faaacf34cf978a52dbc6915ec11e27611cd web
https://github.com/XML-Security/signxml package