EUVD-2026-65138Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
Network-delivered JWT bypass with no auth required, but AC:H because crafting a validly-signed token with array-typed iss is a meaningful prerequisite; I:H for authentication bypass, C:L for incidental resource access, A:N.
Primary rating from Vendor (github).
CVSS VectorVendor: github
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N
Lifecycle Timeline
3DescriptionCVE.org
joserfc is a Python library that provides an implementation of several JSON Object Signing and Encryption (JOSE) standards. Prior to version 1.7.3, JWTClaimsRegistry applies membership matching to list-valued iss and sub claims, allowing an array-valued iss that contains the expected issuer to pass an intended equality check and enabling issuer-validation bypass. This issue is fixed in version 1.7.3.
AnalysisAI
Issuer-validation bypass in joserfc (Python JOSE library) prior to version 1.7.3 allows an attacker to craft a JWT with an array-valued iss claim - e.g., ["expected-issuer"] - that passes the JWTClaimsRegistry equality check via Python membership matching (in operator on a list) rather than strict string equality. The same flaw affects sub claim validation. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires three concurrent conditions. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 3.1 vector (AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:H/A:N) scores 6.5 (Medium), which is reasonable. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker who can construct or obtain a JWT (e.g., from an issuer they control, or by forging one with a known/weak secret) sets the `iss` claim to an array such as `["https://trusted-idp.example.com"]` instead of the expected string. When the application passes this token to `JWTClaimsRegistry.validate()`, the pre-fix membership check finds the expected issuer string inside the array and accepts it as valid, bypassing issuer binding and potentially granting the attacker access scoped to that issuer. … |
| Remediation | Upgrade joserfc to version 1.7.3 or later via `pip install --upgrade joserfc`. … Detailed patch versions, workarounds, and compensating controls in full report. |
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External POC / Exploit Code
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