4.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-27840

CVE-2026-27840: ZITADEL's truncated opaque tokens are still valid

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.

(GitHub Advisory)

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CVE-2026-27840

CVE-2026-27840:

4.3

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/zitadel/zitadel	go	>= 4.0.0, < 4.11.0	4.11.0
github.com/zitadel/zitadel	go	>= 3.0.0, < 3.4.7	3.4.7
github.com/zitadel/zitadel	go	>= 2.31.0, <= 2.71.19
github.com/zitadel/zitadel	go	< 1.80.0-v2.20.0.20260216092519-feab8e1fa371	1.80.0-v2.20.0.20260216092519-feab8e1fa371

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability allows a truncated opaque access token to be considered valid. The root cause is that the user_id from the token payload was not being validated against the user ID from the session data stored in the database. The provided patch feab8e1fa371f3ad654640fc869b2c14f2fdb602 modifies internal/authz/repository/eventsourcing/eventstore/token_verifier.go. The function verifyAccessTokenV2 is changed to accept a subject parameter, which is the user ID from the token. A new check is added to this function to compare this subject with the UserID from the activeToken (retrieved from the database). If they don't match, an "invalid token" error is thrown. The calling function, VerifyAccessToken, is also updated to extract the subject from the token and pass it to verifyAccessTokenV2. Therefore, both VerifyAccessToken and verifyAccessTokenV2 are the key functions involved in this vulnerability and its fix. During exploitation, a call to VerifyAccessToken would be present in the runtime profile, which in turn calls verifyAccessTokenV2.

Vulnerable functions

TokenVerifierRepo.VerifyAccessToken

internal/authz/repository/eventsourcing/eventstore/token_verifier.go

This function is the entry point for access token verification. It was modified to extract the `subject` (user ID) from the token and pass it to `verifyAccessTokenV2` for validation. The original implementation called `verifyAccessTokenV2` without the `subject`, leading to the bypass of the user ID check.

TokenVerifierRepo.verifyAccessTokenV2

internal/authz/repository/eventsourcing/eventstore/token_verifier.go

The vulnerability lies in the `verifyAccessTokenV2` function, which, prior to the patch, did not validate the `user_id` from the decrypted token against the `user_id` stored in the session data in the database. An attacker could provide a truncated v2 access token without the `user_id`, and the system would still accept it, as the `user_id` was retrieved from the database session rather than being verified against the token's content. The patch introduces a check to ensure the `user_id` from the token (`subject`) matches the one from the database (`activeToken.UserID`).

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WAF Rule

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Reasoning

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