CVE-2026-75759 Encrypted ID token or JARM response accepted without a nested signature in erlef oidcc
An attacker can impersonate any user by sending an encrypted but unsigned ID token or JARM response, bypassing signature verification in the oidcc library.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-75759?
CVE-2026-75759 is a high-severity authentication bypass vulnerability in erlef oidcc, published on 30 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-347
Which versions are affected by CVE-2026-75759?
1 open source package ship an affected version, including oidcc.
| Package | Affected | Fixed in |
|---|---|---|
oidcc Hex | From 3.2.0-beta.1 | 3.9.0 |
How do I fix CVE-2026-75759?
Upgrade oidcc to 3.9.0 or later.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-75759 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-75759 exists.
Sources
Also known as EEF-CVE-2026-75759, GHSA-533g-4vf3-xwrj.