User Impersonation Affecting joserfc package, versions [,1.7.3)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PYTHON-JOSERFC-19256806
- published25 Aug 2026
- disclosed24 Aug 2026
- creditkpatsakis
Introduced: 24 Aug 2026
NewCVE-2026-75509 (opens in a new tab)How to fix?
Upgrade joserfc to version 1.7.3 or higher.
Overview
Affected versions of this package are vulnerable to User Impersonation through the JWTClaimsRegistry in src/joserfc/_rfc7519/claims.py. An attacker can make a JWT with an array-typed iss claim pass an exact-issuer check by supplying a list that contains the expected issuer string. Applications that rely on iss or sub validation can accept attacker-supplied tokens as if they were issued by the trusted party, leading to unauthorized token acceptance and downstream access to protected functionality.