CVE-2026-27840: ZITADEL is an open source identity management platform. Starting in version 2.31.0 and prior to versions 3.4.7 and 4.11.0, opaque OIDC access tokens i...

Description

ZITADEL is an open source identity management platform. Starting in version 2.31.0 and prior to versions 3.4.7 and 4.11.0, opaque OIDC access tokens in the v2 format truncated to 80 characters are still considered valid. Zitadel uses a symmetric AES encryption for opaque tokens. The cleartext payload is a concatenation of a couple of identifiers, such as a token ID and user ID. Internally Zitadel has 2 different versions of token payloads. v1 tokens are no longer created, but are still verified as to not invalidate existing session after upgrade. The cleartext payload has a format of `<token_id>:<user_id>`. v2 tokens distinguished further where the `token_id` is of the format `v2_<oidc_session_id>-at_<access_token_id>`. V1 token authZ/N session data is retrieved from the database using the (simple) `token_id` value and `user_id` value. The `user_id` (called `subject` in some parts of our code) was used as being the trusted user ID. V2 token authZ/N session data is retrieved from the database using the `oidc_session_id` and `access_token_id` and in this case the `user_id` from the token is ignored and taken from the session data in the database. By truncating the token to 80 chars, the user_id is now missing from the cleartext of the v2 token. The back-end still accepts this for above reasons. This issue is not considered exploitable, but may look awkward when reproduced. The patch in versions 4.11.0 and 3.4.7 resolves the issue by verifying the `user_id` from the token against the session data from the database. No known workarounds are available.

Metrics

CVSS 3.1

4.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

EPSS Probability

0.14%

3.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-302

Affected Software

Vendor	Product	Versions
Zitadel	Zitadel	>= 2.31.0, <= 2.71.19
Zitadel	Zitadel	>= 3.0.0, < 3.4.7
Zitadel	Zitadel	>= 4.0.0, < 4.11.0

References

https://github.com/zitadel/zitadel/releases/tag/v3.4.7Release Notes
https://github.com/zitadel/zitadel/releases/tag/v4.11.0Release Notes
https://github.com/zitadel/zitadel/security/advisories/GHSA-6mq3-xmgp-pjm5Vendor Advisory

Timeline

Published: Feb 26, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-27840?

ZITADEL is an open source identity management platform. Starting in version 2.31.0 and prior to versions 3.4.7 and 4.11.0, opaque OIDC access tokens in the v2 format truncated to 80 characters are still considered valid. Zitadel uses a symmetric AES encryption for opaque tokens. The cleartext payload is a concatenation of a couple of identifiers, such as a token ID and user ID. Internally Zitadel has 2 different versions of token payloads. v1 tokens are no longer created, but are still verified as to not invalidate existing session after upgrade. The cleartext payload has a format of `<token_id>:<user_id>`. v2 tokens distinguished further where the `token_id` is of the format `v2_<oidc_session_id>-at_<access_token_id>`. V1 token authZ/N session data is retrieved from the database using the (simple) `token_id` value and `user_id` value. The `user_id` (called `subject` in some parts of our code) was used as being the trusted user ID. V2 token authZ/N session data is retrieved from the database using the `oidc_session_id` and `access_token_id` and in this case the `user_id` from the token is ignored and taken from the session data in the database. By truncating the token to 80 chars, the user_id is now missing from the cleartext of the v2 token. The back-end still accepts this for above reasons. This issue is not considered exploitable, but may look awkward when reproduced. The patch in versions 4.11.0 and 3.4.7 resolves the issue by verifying the `user_id` from the token against the session data from the database. No known workarounds are available.

How severe is CVE-2026-27840?

CVE-2026-27840 has a CVSS score of 4.3/10 (MEDIUM severity). The EPSS model estimates a 0.14% probability of exploitation in the next 30 days.

How do I fix CVE-2026-27840?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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