CVE-2026-6966
Signature Threshold Bypass in awslabs/tough Delegated Roles
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- High
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- High
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
Signature Threshold Bypass in awslabs/tough Delegated Roles
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.
- Record
CVE-2026-6966- CVSS 4.0
- 7.0 High
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 - CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N - Weakness
- CWE-347
- Updated
- 2026-11-02
EUVDEUVD-2026-25627
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.
- Record
EUVD-2026-25627- CVSS 4.0
- 7.0 High
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 - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-8m7c-8m39-rv4x
awslabs/tough Delegated Roles have a Signature Threshold Bypass
Summary
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.
Impact
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.
Patches
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.
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
- Record
GHSA-8m7c-8m39-rv4x- CVSS 4.0
- 7.0 High
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 - CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N - Weakness
- CWE-347
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2026-6966- CVSS 4.0
- 7.0 High
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X - CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N - CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N - Weakness
- CWE-347
- Updated
- 2026-11-02
OSV
Signature Threshold Bypass in awslabs/tough Delegated Roles
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.
- Record
CVE-2026-6966- CVSS 4.0
- 7.0 High
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 - Weakness
- CWE-347
- Updated
- 2026-11-07
OSVGHSA-8m7c-8m39-rv4x
awslabs/tough Delegated Roles have a Signature Threshold Bypass
Summary
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.
Impact
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.
Patches
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.
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
- Record
GHSA-8m7c-8m39-rv4x- CVSS 4.0
- 7.0 High
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 - CVSS 3.1
- 5.3 Medium
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:H/A:N - Weakness
- CWE-347
- Updated
- 2026-11-02
Affected products
Affected packages
History
| Recorded | Changed | Sources |
|---|---|---|
| facts | OSV | |
| first indexed | CVE List, EUVD, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-6966 is a high vulnerability (CVSS 7.0) in Amazon Tough, published April 24, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.28%, the 20th percentile. Fixed in tough 0.22.0.
