title: CL-Signatures Revocation Scheme in Ursa has flaws that allow a holder to demonstrate non-revocation of a revoked credential
description: Ursa is a cryptographic library for use with blockchains. 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. A verifier may verify a credential from a holder as being "not revoked" when in fact, the holder's credential has been revoked. Ursa has moved to end-of-life status and no fix is expected.
problem types: CWE-327: Use of a Broken or Risky Cryptographic Algorithm
affected:
{
vendor: hyperledger-archives
product: ursa
versions:
version: <= 0.3.7, status: affected
}
metrics:
cvssV3_1: [
attackComplexity: HIGH
attackVector: PHYSICAL
availabilityImpact: NONE
baseScore: 6.5
baseSeverity: MEDIUM
confidentialityImpact: HIGH
integrityImpact: HIGH
privilegesRequired: HIGH
scope: CHANGED
userInteraction: REQUIRED
vectorString: CVSS:3.1/AV:P/AC:H/PR:H/UI:R/S:C/C:H/I:H/A:N
version: 3.1
]