Authentication Bypass in GnuTLS via RSA-PSK NUL Character

Compliance Impact

The vulnerability allows an attacker to bypass authentication and gain unauthorized access to systems using GnuTLS with RSA-PSK configuration. Such unauthorized access can lead to exposure or compromise of sensitive data, which may result in non-compliance with data protection regulations like GDPR and HIPAA that require strict access controls and protection of personal or health information.

Therefore, this flaw could negatively impact compliance with common standards and regulations by undermining authentication mechanisms and potentially exposing protected data.

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Mitigation Strategies

To mitigate the CVE-2026-42010 vulnerability, you should update GnuTLS to a version where the username comparison logic has been corrected to properly handle NUL characters in usernames.

This fix prevents authentication bypass by ensuring usernames are fully compared rather than truncated at NUL characters.

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Executive Summary

The CVE-2026-42010 vulnerability in GnuTLS is an authentication bypass issue. It occurs because servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) incorrectly match usernames that contain a NUL character with truncated versions of those usernames. This improper handling of NUL characters in usernames allows a remote attacker to send a specially crafted username and bypass the authentication process.

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Impact Analysis

This vulnerability can allow an attacker to gain unauthorized access to a system by circumventing the authentication process. Because the server incorrectly matches usernames containing NUL characters with truncated usernames, an attacker can exploit this flaw to bypass authentication controls, potentially leading to unauthorized access to sensitive data or system functions.

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