# CVE-2026-42010: GnuTLS authentication bypass in RSA-PSK username handling

Source: https://junglewise.ai/threats/cve-2026-42010-gnutls-authentication-bypass-in-rsa-psk-username-handling  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-07. Updated: 2026-05-27  
License: CC BY 4.0 with a link back

CVE-2026-42010 · Severity: high · CVSS 7.1 · Published 2026-05-07

A security flaw was found in GnuTLS, a widely used library that provides secure communication for applications and servers. When a server is configured to use a specific type of secure key (RSA-PSK), it may incorrectly validate usernames that contain special hidden characters. This could allow an unauthorized person to bypass the login process and gain access to the system without a valid password.

Technologies: [Red Hat Enterprise Linux 10](https://junglewise.ai/threats/technologies/enterprise-linux-10), [Red Hat Enterprise Linux 8](https://junglewise.ai/threats/technologies/enterprise-linux-8), [Red Hat Enterprise Linux 9](https://junglewise.ai/threats/technologies/enterprise-linux-9). Vendors: [Red Hat](https://junglewise.ai/threats/vendors/red-hat).

## Quick answers

**Is CVE-2026-42010 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-42010 being exploited in the wild.

**How severe is CVE-2026-42010?** High severity, with a CVSS score of 7.1, published 7 May 2026.

**Which products and versions are affected?** Red Hat Enterprise Linux 10 10.0; Red Hat Enterprise Linux 8 8.10; Red Hat Enterprise Linux 9 9.0.

**Is there a fix for CVE-2026-42010?** A patch was published on 2026-05-26: Red Hat released updated packages for RHEL 8, 9, and 10 Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-42010 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-42010?** Check whether you run Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 or Red Hat Enterprise Linux 9 at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A vulnerability classified as a Null Byte Interaction Error (CWE-626) exists in GnuTLS. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) incorrectly match usernames containing a NUL character with truncated versions of those usernames. This occurs because the comparison logic fails to validate the full length of the username string, stopping at the NUL byte. A remote, unauthenticated attacker can exploit this by sending a crafted username to bypass authentication mechanisms. Red Hat has released patches for various Enterprise Linux versions (8, 9, and 10) to address this by ensuring comparisons are performed up to the full username length.

## Affected products

- GNU GnuTLS versions prior to 3.8.13-1
- Red Hat Enterprise Linux 8 8.10
- Red Hat Enterprise Linux 9 9.0
- Red Hat Enterprise Linux 10 10.0
- Red Hat Hardened Images -

## Timeline

- 2026-05-02: advisory: Initial Red Hat security advisory RHSA-2026:13274 issued
- 2026-05-07: disclosed: CVE-2026-42010 published to NVD
- 2026-05-26: patched: Red Hat released updated packages for RHEL 8, 9, and 10

## References

- [https://access.redhat.com/errata/RHSA-2026:13274](https://access.redhat.com/errata/RHSA-2026:13274)
- [https://access.redhat.com/errata/RHSA-2026:20611](https://access.redhat.com/errata/RHSA-2026:20611)
- [https://access.redhat.com/security/cve/CVE-2026-42010](https://access.redhat.com/security/cve/CVE-2026-42010)
- [https://bugzilla.redhat.com/show_bug.cgi?id=2467289](https://bugzilla.redhat.com/show_bug.cgi?id=2467289)

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