SignXML's signature verification with HMAC is vulnerable to an algorithm confusion 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 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 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-6vx8-pcwv-xhf4
- https://nvd.nist.gov/vuln/detail/CVE-2025-48994
- https://github.com/XML-Security/signxml/commit/e3c0c2b82a3329a65d917830657649c98b8c7600
- https://github.com/XML-Security/signxml
- https://pypi.org/project/signxml
- https://github.com/advisories/GHSA-6vx8-pcwv-xhf4
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-303- Platform
- Python (PyPI)
- Package
signxml- Disclosed
- 05.06.2025
- Updated
- 11.10.2026 13:19
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1921 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-6vx8-pcwv-xhf4 - 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 an algorithm confusion attack this entry
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