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CL-Signatures Revocation Scheme in Ursa has flaws that allow a holder to demonstrate non-revocation of a revoked credential

Moderate severity GitHub Reviewed Published Jan 16, 2024 in hyperledger-archives/ursa • Updated Jan 19, 2024

Package

cargo anoncreds-clsignatures (Rust)

Affected versions

< 0.1.0

Patched versions

None
cargo ursa (Rust)
<= 0.3.7
None

Description

Summary

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.

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  • A verifier may verify a credential from a holder as being "not revoked" when in fact, the holder's credential has been revoked.

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.

References

@swcurran swcurran published to hyperledger-archives/ursa Jan 16, 2024
Published to the GitHub Advisory Database Jan 16, 2024
Reviewed Jan 16, 2024
Published by the National Vulnerability Database Jan 16, 2024
Last updated Jan 19, 2024

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Physical
Attack complexity
High
Privileges required
High
User interaction
Required
Scope
Changed
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:P/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N

EPSS score

0.091%
(40th percentile)

Weaknesses

CVE ID

CVE-2024-21670

GHSA ID

GHSA-r78f-4q2q-hvv4
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