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9.1
CVE-2026-75759: erlef OIDC library may accept fake encrypted login tokens
CVE-2026-75759 · published 4 days ago
Summary
The erlef OIDC software that handles single‑sign‑on can treat an encrypted login token that lacks a proper signature (proof it really came from the trusted source) as valid. This allows an attacker to create a token and log in as any user. Upgrade the library to version 3.9.0 or later (or apply the vendor’s patch) and configure it to require signed tokens.
What to do
- Update oidcc to version 3.9.0.
Affected software
| Ecosystem | Vendor | Product | Affected versions |
|---|---|---|---|
| – | erlef | oidcc |
< 3.9.0 < 5f62fbccdae8526ff62653b8901657a6c1400fd9 |
| Hex | – | oidcc |
>= 3.2.0-beta.1, < 3.9.0 Fix: upgrade to 3.9.0
|
Original advisory text
Encrypted ID token or JARM response accepted without a nested signature in erlef oidcc
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.
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.
References
- https://github.com/erlef/oidcc/security/advisories/GHSA-533g-4vf3-xwrj related vendor-advisory
- https://cna.erlef.org/cves/CVE-2026-75759.html related
- https://osv.dev/vulnerability/EEF-CVE-2026-75759 related
- https://github.com/erlef/oidcc/commit/5f62fbccdae8526ff62653b8901657a6c1400fd9 patch
- https://hex.pm/packages/oidcc Product
- https://github.com URL
- https://repo.hex.pm URL
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/75xxx/CVE-2026-75759... Vendor Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-75759 Vendor Advisory
- https://github.com/erlef/oidcc Product
Severity
9.1
Critical
Exploitation
EPSS <1%
Type
CWE-347Improper Verification of Cryptographic Signature
Timeline
Published30 Aug 2026
Updated2 Sep 2026
First seen30 Aug 2026
Sources
CVE-2026-75759 · NVD
CVE-2026-75759 · MITRE
EEF-CVE-2026-75759 · OSV
GHSA-533g-4vf3-xwrj · GHSA
CVE-2026-75759 · OSV
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