Description
Improper Verification of Cryptographic Signature vulnerability in erlef oidcc allows an unauthenticated attacker to impersonate an arbitrary user via an encrypted ID token or JARM response carrying no nested signature. OpenID Connect Core 1.0 section 2 requires that an encrypted ID token be signed then encrypted, with the result being a Nested JWT, and JARM processing rule 5 requires the client to check the signature unconditionally. oidcc instead accepted a JWE wrapping unsigned claims as fully validated, so anyone holding the relying party's public encryption key could mint a token with an arbitrary sub, iss, and aud without possessing the provider's signing key.

In oidcc_jwt_util:verify_decrypted_token/4, a decrypted payload that is not a signed JWS fell back to parsing the plaintext claims and returning them with no verifying key. oidcc_token:int_validate_jwt/4 then matched on the JOSE structure type rather than on whether a signature had been verified, and returned success. The JARM path in oidcc_token:validate_jarm/3 is reachable through the browser front channel. UserInfo responses are not affected, because OpenID Connect Core 1.0 section 5.3.2 permits them to be encrypted without also being signed.

This issue affects oidcc: from 3.2.0-beta.1 before 3.9.0.
Published: 2026-08-30
Score: 7.6 High
EPSS: < 1% Very Low
KEV: No
Impact: Identity Spoofing
Action: Immediate Patch
AI Analysis

Impact

The flaw in erlef’s oidcc library permits an unauthenticated adversary to forge an encrypted ID token or JARM response that lacks a nested signature. The library accepts a JWE that wraps unsigned claims as completely validated, enabling the attacker to craft a token with arbitrary subject, issuer, and audience fields. An attacker possessing the relying party’s public encryption key can therefore create a spoofed token granting denial of legitimate user identity and enabling session hijacking or unauthorized access to protected resources.

Affected Systems

vulnerable releases are erlef’s oidcc starting at 3.2.0-beta.1 up to, but not including, 3.9.0. Both variants listed in the CNA affect this range.

Risk and Exploitability

The CVSS score of 7.6 indicates high severity, whereas the EPSS score is unavailable, and the vulnerability is not currently listed in CISA’s KEV catalog. The weakness is exploitable remotely through the browser front‑channel path used by JARM; any party able to supply a crafted JWE that can be decrypted with the relying party’s public key can impersonate an arbitrary user without possessing the provider’s signing key, which meets the conditions outlined in OpenID Connect Core 1.0.

Generated by OpenCVE AI on August 30, 2026 at 02:20 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade erlef oidcc to version 3.9.0 or later, which contains the signature verification fix.
  • If an immediate upgrade is not possible, disable or configure the library to reject unsigned JWE payloads and enforce signature verification before decryption.
  • Introduce runtime checks that require a valid JWS signature on all incoming ID tokens and JARM responses before processing them.

Generated by OpenCVE AI on August 30, 2026 at 02:20 UTC.

Tracking

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Advisories

No advisories yet.

History

Mon, 31 Aug 2026 21:30:00 +0000

Type Values Removed Values Added
First Time appeared Erlef oidcc Plug
Vendors & Products Erlef oidcc Plug

Mon, 31 Aug 2026 15:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Sun, 30 Aug 2026 01:45:00 +0000

Type Values Removed Values Added
Description Improper Verification of Cryptographic Signature vulnerability in erlef oidcc allows an unauthenticated attacker to impersonate an arbitrary user via an encrypted ID token or JARM response carrying no nested signature. OpenID Connect Core 1.0 section 2 requires that an encrypted ID token be signed then encrypted, with the result being a Nested JWT, and JARM processing rule 5 requires the client to check the signature unconditionally. oidcc instead accepted a JWE wrapping unsigned claims as fully validated, so anyone holding the relying party's public encryption key could mint a token with an arbitrary sub, iss, and aud without possessing the provider's signing key. In oidcc_jwt_util:verify_decrypted_token/4, a decrypted payload that is not a signed JWS fell back to parsing the plaintext claims and returning them with no verifying key. oidcc_token:int_validate_jwt/4 then matched on the JOSE structure type rather than on whether a signature had been verified, and returned success. The JARM path in oidcc_token:validate_jarm/3 is reachable through the browser front channel. UserInfo responses are not affected, because OpenID Connect Core 1.0 section 5.3.2 permits them to be encrypted without also being signed. This issue affects oidcc: from 3.2.0-beta.1 before 3.9.0.
Title Encrypted ID token or JARM response accepted without a nested signature in erlef oidcc
First Time appeared Erlef
Erlef oidcc
Weaknesses CWE-347
CPEs cpe:2.3:a:erlef:oidcc:*:*:*:*:*:*:*:*
Vendors & Products Erlef
Erlef oidcc
References
Metrics cvssV4_0

{'score': 7.6, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:P/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N'}

Subscriptions

Erlef Oidcc Oidcc Plug
cve-icon MITRE

Status: PUBLISHED

Assigner: EEF

Published:

Updated: 2026-08-31T14:53:35.902Z

Reserved: 2026-08-21T09:30:01.395Z

Link: CVE-2026-75759

cve-icon Vulnrichment

Updated: 2026-08-31T14:53:30.342Z

cve-icon NVD

Status : Deferred

Published: 2026-08-30T02:18:30.110

Modified: 2026-09-01T21:15:00.147

Link: CVE-2026-75759

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-08-31T21:15:05Z

Weaknesses
  • CWE-347

    Improper Verification of Cryptographic Signature