CVE-2025-48995 SignXML's signature verification with HMAC is vulnerable to a timing attack
Attackers can exploit timing differences to reconstruct HMAC keys in SignXML when X509 validation is disabled, compromising signature integrity.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-48995?
CVE-2025-48995 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 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.
Weakness: CWE-208
Which versions are affected by CVE-2025-48995?
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-2025-48995?
Upgrade signxml to 4.0.4 or later.
Is CVE-2025-48995 being exploited?
There is no known exploitation of CVE-2025-48995 in the wild and no public exploit code.
Sources
Also known as DEBIAN-CVE-2025-48995, GHSA-gmhf-gg8w-jw42, PYSEC-2026-1922, UBUNTU-CVE-2025-48995.