What’s Vulnerable › Vulnerabilities

CVE-2025-48995: SignXML's signature verification with HMAC is vulnerable to a timing 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-208

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 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.

Affected products

• XML-Security signxml: before 4.0.4

References

• https://github.com/XML-Security/signxml/commit/1b501faaacf34cf978a52dbc6915ec11e27611cd
• https://github.com/XML-Security/signxml/security/advisories/GHSA-gmhf-gg8w-jw42

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