CVE-2025-66016: cggmp21 has a missing check in the ZK proof used in CGGMP21

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.2%, percentile 8: FIRST’s model estimates a 0.2% chance of exploitation activity in the next 30 days, higher than 8% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes cggmp21 (crates.io (Rust)) < 0.6.3, fixed in 0.6.3; cggmp24 (crates.io (Rust)) < 0.7.0-alpha.2, fixed in 0.7.0-alpha.2. Check your lockfile, including transitive dependencies.

What it is

CGGMP24 is a state-of-art ECDSA TSS protocol that supports 1-round signing (requires 3 preprocessing rounds), identifiable abort, and a key refresh protocol. Prior to version 0.6.3, there is a missing check in the ZK proof that enables an attack in which single malicious signer can reconstruct full private key. This issue has been patched in version 0.6.3, for full mitigation it is recommended to upgrade to cggmp24 version 0.7.0-alpha.2 as it contains more security checks.

From the GitHub advisory

Impact cggmp21 concerns a missing check in the ZK proof that enables an attack in which a single malicious signer can reconstruct full private key.

Patches cggmp21 v0.6.3 is a patch release that contains a fix that introduces this specific missing check However, cggmp21 recommends upgrading to cggmp24 v0.7.0-alpha.2 which contains many other security checks as a precaution. Follow migration guideline to upgrade.

Workarounds Update to cggmp21 v0.6.3, a minor release that contains a minimal security patch.

However, for full mitigation, users will need to upgrade to cggmp24 v0.7.0-alpha.2 as it contains many more security check implementations.

Resources Read this blog post to learn more.

Weakness type: CWE-345, CWE-347.

Product: cggmp21 (crates.io (Rust)) · Assigned by: GitHub_M · Published: 2025-11-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.19% probability of exploitation activity in the next 30 days; percentile 8.

Timeline

• 2025-11-25 — CVE record last updated
• 2025-11-25 — CVE record published by GitHub_M
• 2025-11-25 — GitHub-reviewed advisory GHSA-m95p-425x-x889 published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-m95p-425x-x889 github.com
2. CVE.org record CVE-2025-66016 cve.org
3. NVD entry CVE-2025-66016 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. dfns.co dfns.co
3. github.com github.com
4. rustsec.org rustsec.org
5. rustsec.org rustsec.org

Critical crates.io (Rust) advisories · Today’s Security Digest