Summary
CL-Signatures Revocation Scheme in Ursa has flaws that allow a holder to demonstrate non-revocation of a revoked credential
The revocation schema that is part of the Ursa CL-Signatures implementations has a flaw that could impact the privacy guarantees defined by the AnonCreds verifiable credential model, allowing a malicious holder of a revoked credential to generate a valid Non-Revocation Proof for that credential as part of an AnonCreds presentation.
Details
The revocation schema that is part of the Ursa CL-Signatures implementation has a flaw that could impact the privacy guarantees defined by the AnonCreds verifiable credential model, allowing a malicious holder of a revoked credential to generate a valid Non-Revocation Proof for that credential as part of an AnonCreds presentation.
The flaw exists in all CL-Signature versions published from the Hyperledger Ursa repository to the Ursa Rust Crate, and are fixed in all versions published from the Hyperledger AnonCreds CL-Signatures repository to the AnonCreds CL-Signatures Rust Crate.
To exploit the flaw, a holder must update their wallet (agent) software, replacing the Hyperledger Ursa or AnonCreds CL-Signatures library that generates the proof of non-revocation. This may involve, for example, altering an iOS or Android application published in the respective app stores. A mitigation for this flaw is to use the application attestation capabilities (such as the Android "SafetyNet Attestation API") offered by the app store vendors to (for example) "help determine whether your servers are interacting with your genuine app running on a genuine Android device."
The problem is created in the generation of a revocation registry, prior to issuing any credentials. As such, to eliminate the impact of the flaw, the issued credentials must be re-issued based on a correct revocation registry, generated from a correct implementation, such as Hyperledger AnonCreds CL-Signatures.
Mitigation
Upgrade libraries/applications using the Ursa Rust Crate to any version of the AnonCreds CL-Signatures Rust Crate. If your application has issued revocable credentials, once the Issuer library has been upgraded, new revocation registries must be created, and credentials issued from revocation registries created with the the flawed software must be revoked and reissued.
A verifier can detect if a holder presents a flawed revocable credential.
Impact
The potential impact is as follows:
- A verifier may verify a credential from a holder as being "not revoked" when in fact, the holder's credential has been revoked.
The application uses a cryptographic algorithm known to have weaknesses, such as MD5, SHA-1, or DES. Typical impact: compromised confidentiality or integrity of protected data.
CVE-2024-21670 has a CVSS score of 6.5 (Medium). The vector is requires physical access, high privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. No fixed version is listed yet, so configuration controls and monitoring matter more in the interim.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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In the interim: Replace the broken algorithm with a current recommendation: SHA-256 or higher for hashing, AES-GCM for symmetric encryption.
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2024-21670? CVE-2024-21670 is a medium-severity use of a broken or risky cryptographic algorithm vulnerability in ursa (rust), affecting versions <= 0.3.7. No fixed version is listed yet. The application uses a cryptographic algorithm known to have weaknesses, such as MD5, SHA-1, or DES.
- How severe is CVE-2024-21670? CVE-2024-21670 has a CVSS score of 6.5 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which packages are affected by CVE-2024-21670?
ursa(rust) (versions <= 0.3.7)anoncreds-clsignatures(rust) (versions < 0.1.0)
- Is there a fix for CVE-2024-21670? No fixed version is listed for CVE-2024-21670 yet. Monitor the advisory for updates and apply mitigations in the interim.
- Is CVE-2024-21670 exploitable, and should I be worried? Whether CVE-2024-21670 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2024-21670 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2024-21670? No fixed version is listed yet. In the interim: Replace the broken algorithm with a current recommendation: SHA-256 or higher for hashing, AES-GCM for symmetric encryption.