# CVE-2026-6966: Signature Threshold Bypass in awslabs/tough Delegated Roles

> Attackers can bypass TUF signature thresholds by duplicating signatures, allowing acceptance of forged delegated role metadata in the tough library.

- **Severity:** High 7.0 (`CVSS:4.0/AV:N/AC:H/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:H/SA: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:** 24 Apr 2026
- **Updated:** 20 Oct 2026
- **Also known as:** GHSA-8m7c-8m39-rv4x

## What is CVE-2026-6966?

CVE-2026-6966 is a high-severity vulnerability in AWS tough, published on 24 Apr 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

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.

We recommend you upgrade to tough-v0.22.0 / tuftool-v0.15.0.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2026-6966?

4 open source packages ship an affected version, including tough and tuftool. It affects 2 products.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `tough` | crates.io | All versions | 0.22.0 |
| `tough` | crates.io | All versions | 0.22.0 |
| `tuftool` | crates.io | All versions | 0.15.0 |
| `tuftool` | crates.io | All versions | 0.15.0 |

Products: Amazon Tough, Amazon Tuftool.

## How do I fix CVE-2026-6966?

Upgrade tough to 0.22.0 or later.

## Is CVE-2026-6966 being exploited?

There is no known exploitation of CVE-2026-6966 in the wild and no public exploit code.

## Other vulnerabilities in AWS tough

- [CVE-2020-15093](https://insights.sbomify.com/CVE-2020-15093/): Improper verification of signature threshold in tough (high 8.6)
- [CVE-2021-41149](https://insights.sbomify.com/CVE-2021-41149/): Improper sanitization of target names in tough (high 8.2)
- [CVE-2021-41150](https://insights.sbomify.com/CVE-2021-41150/): Improper sanitization of delegated role names in tough (high 8.2)
- [CVE-2026-6967](https://insights.sbomify.com/CVE-2026-6967/): Missing Delegated Metadata Validation in awslabs/tough (high 7.1)
- [CVE-2026-6968](https://insights.sbomify.com/CVE-2026-6968/): Multiple Path Traversal Variants in awslabs/tough (high 7.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6966 and fix it if it is affected.

What it is: CVE-2026-6966 is a high-severity vulnerability in AWS tough, published on 24 Apr 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-2026-6966 in the wild and no public exploit code.

Affected packages and fixed versions:
- tough (crates.io): affected all versions; fixed in 0.22.0
- tough (crates.io): affected all versions; fixed in 0.22.0
- tuftool (crates.io): affected all versions; fixed in 0.15.0
- tuftool (crates.io): affected all versions; fixed in 0.15.0

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-2026-6966/ (Markdown: https://insights.sbomify.com/CVE-2026-6966/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6966
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6966
- OSV: https://osv.dev/vulnerability/CVE-2026-6966

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6966/
Summaries are generated and may contain mistakes; the official description above is the record.