XML-Security signxml up to 4.0.3 timing discrepancy

Summaryinfo

A vulnerability labeled as problematic has been found in XML-Security signxml up to 4.0.3. This vulnerability affects unknown code. Executing a manipulation can lead to timing discrepancy. This vulnerability is tracked as CVE-2025-48995. The attack can be launched remotely. No exploit exists. The affected component should be upgraded.

Detailsinfo

A vulnerability classified as problematic was found in XML-Security signxml up to 4.0.3. This vulnerability affects an unknown part. The manipulation with an unknown input leads to a timing discrepancy vulnerability. The CWE definition for the vulnerability is CWE-208. Two separate operations in a product require different amounts of time to complete, in a way that is observable to an actor and reveals security-relevant information about the state of the product, such as whether a particular operation was successful or not. As an impact it is known to affect confidentiality. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2025-48995 since 05/29/2025. The exploitation appears to be difficult. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available. The MITRE ATT&CK project declares the attack technique as T1592.

The vulnerability scanner Nessus provides a plugin with the ID 264351 (Linux Distros Unpatched Vulnerability : CVE-2025-48995), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 4.0.4 eliminates this vulnerability. Applying the patch 1b501faaacf34cf978a52dbc6915ec11e27611cd is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the vulnerability database at Tenable (264351). Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• XML-Security

Name

• signxml

Version

• 4.0.0
• 4.0.1
• 4.0.2
• 4.0.3

License

• open-source

Website

• Product: https://github.com/XML-Security/signxml/

CPE 2.3info

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CPE 2.2info

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Once again VulDB remains the best source for vulnerability data.

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