CVE-2026-6966

Improper verification of cryptographic signature uniqueness in delegated role validation in awslabs/tough before tough-v0.22.0 allows remote authenticated users to bypass the TUF signature threshold requirement by duplicating a valid signature, causing the client to accept forged delegated role metadata.

Workarounds

No workarounds to this issue are known.

References

• CVE-2026-6966

If there are any questions or comments about this advisory, please contact [AWS/Amazon] Security via the vulnerability reporting page or directly via email to [email protected]. Please do not create a public GitHub issue.

Acknowledgement

Amazon Web Services Labs would like to thank Emily Albini of Oxide Computer and Oleh Konko of 1seal for collaborating on this issue through the coordinated vulnerability disclosure process

The tough library, prior to 0.22.0, does not properly verify the uniqueness of keys in the signatures provided to meet the threshold of cryptographic signatures in delegated targets. It allows actors with access to a valid signing key to create multiple valid signatures in order to circumvent TUF requiring a minimum threshold of unique keys before the metadata is considered valid.

CVE-2026-6966 has a CVSS score of 5.3 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.22.0, 0.15.0); upgrading removes the vulnerable code path.

Kodem intelligence

This issue has been addressed in tough version 0.22.0 and tuftool version 0.15.0. We recommend upgrading to the latest version and ensuring any forked or derivative code is patched to incorporate the new fixes.

1. What is CVE-2026-6966? CVE-2026-6966 is a high-severity security vulnerability in tough (rust), affecting versions < 0.22.0. It is fixed in 0.22.0, 0.15.0.
2. How severe is CVE-2026-6966? CVE-2026-6966 has a CVSS score of 5.3 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-6966?
   • tough (rust) (versions < 0.22.0)
   • tuftool (rust) (versions < 0.15.0)
4. Is there a fix for CVE-2026-6966? Yes. CVE-2026-6966 is fixed in 0.22.0, 0.15.0. Upgrade to this version or later.
5. Is CVE-2026-6966 exploitable, and should I be worried? Whether CVE-2026-6966 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-6966 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-6966?
   • Upgrade tough to 0.22.0 or later
   • Upgrade tuftool to 0.15.0 or later