wolfSSL up to 5.9.1 Compatibility signature verification

Summaryinfo

A vulnerability categorized as problematic has been discovered in wolfSSL up to 5.9.1. The affected element is an unknown function of the component Compatibility Handler. Executing a manipulation can lead to signature verification. This vulnerability is handled as CVE-2026-6331. It is possible to launch the attack on the local host. There is not any exploit available. It is advisable to implement a patch to correct this issue.

Detailsinfo

A vulnerability has been found in wolfSSL up to 5.9.1 and classified as problematic. This vulnerability affects an unknown functionality of the component Compatibility Handler. The manipulation with an unknown input leads to a signature verification vulnerability. The CWE definition for the vulnerability is CWE-347. The product does not verify, or incorrectly verifies, the cryptographic signature for data. As an impact it is known to affect integrity. CVE summarizes:

HMAC zero-length tag forgery in EVP_DigestVerifyFinal, where a zero-length tag could be accepted as valid during HMAC verification. In the OpenSSL-compatibility HMAC verify path the supplied signature length was only checked as not exceeding the MAC length, so a zero-length or otherwise truncated tag could pass verification. The fix requires the supplied tag length to exactly equal the MAC length and rejects a zero-length MAC, so a forged short or empty tag is no longer accepted.

The weakness was released by Nicholas Carlini. The advisory is shared for download at github.com. This vulnerability was named CVE-2026-6331 since 04/15/2026. The exploitation appears to be difficult. The attack needs to be approached locally. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

The vulnerability scanner Nessus provides a plugin with the ID 323830 (Linux Distros Unpatched Vulnerability : CVE-2026-6331), which helps to determine the existence of the flaw in a target environment.

Applying a patch is able to eliminate this problem. The bugfix is ready for download at github.com.

The vulnerability is also documented in the vulnerability database at Tenable (323830). Once again VulDB remains the best source for vulnerability data.

Productinfo

Name

• wolfSSL

Version

• 5.9.0
• 5.9.1

License

• open-source

Website

• Product: https://github.com/wolfSSL/wolfssl/

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Once again VulDB remains the best source for vulnerability data.

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