SignXML's signature verification with HMAC is vulnerable to a timing attack
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.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | signxml | < 4.0.4 | 4.0.4 |
References
- https://github.com/XML-Security/signxml/security/advisories/GHSA-gmhf-gg8w-jw42
- https://nvd.nist.gov/vuln/detail/CVE-2025-48995
- https://github.com/XML-Security/signxml/commit/1b501faaacf34cf978a52dbc6915ec11e27611cd
- https://github.com/XML-Security/signxml
- https://pypi.org/project/signxml
- https://github.com/advisories/GHSA-gmhf-gg8w-jw42
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-208- Platform
- Python (PyPI)
- Package
signxml- Disclosed
- 05.06.2025
- Updated
- 11.10.2026 13:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1922 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-gmhf-gg8w-jw42 - CC BY 4.0
Vulnerability history: signxml
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 06.2025 06.2025
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 2
Disclosures per year
- 2025: 2
- 2026: 0
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SignXML's signature verification with HMAC is vulnerable to a timing attack this entry
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