CVE-2025-48994 SignXML's signature verification with HMAC is vulnerable to an algorithm confusion attack
Attackers can bypass signature verification in SignXML by exploiting algorithm confusion when X509 validation is disabled and HMAC keys are used.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-48994?
CVE-2025-48994 is a medium-severity vulnerability in XML-Security signxml, published on 2 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-303
Which versions are affected by CVE-2025-48994?
3 open source packages ship an affected version, including signxml.
| Package | Affected | Fixed in |
|---|---|---|
signxml PyPI | All versions | 4.0.4 |
signxml PyPI | All versions | 4.0.4 |
signxml PyPI | All versions | 4.0.4 |
How do I fix CVE-2025-48994?
Upgrade signxml to 4.0.4 or later.
Is CVE-2025-48994 being exploited?
There is no known exploitation of CVE-2025-48994 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2025-48994, GHSA-6vx8-pcwv-xhf4, PYSEC-2026-1921, UBUNTU-CVE-2025-48994.