# CVE-2026-42010: Gnutls: gnutls: authentication bypass via nul character in username

> Remote attackers can bypass authentication in GnuTLS servers using RSA-PSK by exploiting NUL character handling in usernames.

- **Severity:** High 7.1 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 May 2026
- **Updated:** 26 Oct 2026
- **Also known as:** ALPINE-CVE-2026-42010, AZL-86775, BELL-CVE-2026-42010, CLSA-2026-1778934026, CLSA-2026-1779183792, CLSA-2026-1779272835, CLSA-2026-1779744941, CLSA-2026-1779869625, CLSA-2026-1779881448, DEBIAN-CVE-2026-42010, ECHO-8172-5400-ef47, GHSA-m3r7-xjq8-gc4r

## What is CVE-2026-42010?

CVE-2026-42010 is a high-severity authentication bypass vulnerability in Gnu Gnutls, published on 7 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A flaw was found in gnutls. Servers configured with RSA-PSK (Rivest–Shamir–Adleman – Pre-Shared Key) wrongfully matched usernames containing a NUL character with truncated usernames. A remote attacker could exploit this by sending a specially crafted username, leading to an authentication bypass. This vulnerability allows an attacker to gain unauthorized access by circumventing the authentication process.

Weakness: CWE-626 (Null Byte Interaction Error (Poison Null Byte)), CWE-170 (Improper Null Termination)

## Which versions are affected by CVE-2026-42010?

It affects 4 products.


Products: Gnu Gnutls, Redhat Enterprise Linux, Redhat Hardened Images, Redhat Openshift Container Platform.

## How do I fix CVE-2026-42010?

Apply the vendor's patch.

## Is CVE-2026-42010 being exploited?

There is no known exploitation of CVE-2026-42010 in the wild and no public exploit code.

## Other vulnerabilities in Gnu Gnutls

- [CVE-2008-1948](https://insights.sbomify.com/CVE-2008-1948/): Memory corruption in n/a (critical 10.0)
- [CVE-2017-5334](https://insights.sbomify.com/CVE-2017-5334/): Use after free in n/a (critical 9.8)
- [CVE-2017-5336](https://insights.sbomify.com/CVE-2017-5336/): Memory corruption in n/a (critical 9.8)
- [CVE-2017-5337](https://insights.sbomify.com/CVE-2017-5337/): Memory corruption in n/a (critical 9.8)
- [CVE-2008-1949](https://insights.sbomify.com/CVE-2008-1949/): Null dereference in n/a (critical 9.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42010 and fix it if it is affected.

What it is: CVE-2026-42010 is a high-severity authentication bypass vulnerability in Gnu Gnutls, published on 7 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-42010 in the wild and no public exploit code.

Affected product: Gnu Gnutls. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42010/ (Markdown: https://insights.sbomify.com/CVE-2026-42010/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42010
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42010
- OSV: https://osv.dev/vulnerability/CVE-2026-42010

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42010/
Summaries are generated and may contain mistakes; the official description above is the record.