What’s Vulnerable › Vulnerabilities

CVE-2025-48994: SignXML's signature verification with HMAC is vulnerable to an algorithm confusion attack

• Severity: medium (CVSS 6.9 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-06-02 · updated 2026-06-17
• Weakness: CWE-303

Description

SignXML is an implementation of the W3C XML Signature standard in Python. When verifying signatures with X509 certificate validation turned off and HMAC shared secret set (`signxml.XMLVerifier.verify(require_x509=False, hmac_key=...`), versions of SignXML prior to 4.0.4 are vulnerable to a potential algorithm confusion attack. Unless the user explicitly limits the expected signature algorithms using the `signxml.XMLVerifier.verify(expect_config=...)` setting, an attacker may supply a signature unexpectedly signed with a key other than the provided HMAC key, using a different (asymmetric key) signature algorithm. Starting with SignXML 4.0.4, specifying `hmac_key` causes the set of accepted signature algorithms to be restricted to HMAC only, if not already restricted by the user.

Affected products

• XML-Security signxml: before 4.0.4

References

• https://github.com/XML-Security/signxml/commit/e3c0c2b82a3329a65d917830657649c98b8c7600
• https://github.com/XML-Security/signxml/security/advisories/GHSA-6vx8-pcwv-xhf4

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