# CVE-2026-27840: ZITADEL's truncated opaque tokens are still valid > Truncated opaque tokens remain valid in ZITADEL, potentially bypassing user ID verification, though currently considered non-exploitable. - **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N`) - **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:** Yes - **Published:** 26 Feb 2026 - **Updated:** 26 Feb 2026 - **Also known as:** GHSA-6mq3-xmgp-pjm5, GO-2026-4573 ## What is CVE-2026-27840? CVE-2026-27840 is a medium-severity authentication bypass vulnerability in zitadel, published on 26 Feb 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 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 `:`. v2 tokens distinguished further where the `token_id` is of the format `v2_-at_`. 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. Weakness: CWE-302 (Authentication Bypass by Assumed-Immutable Data) ## Which versions are affected by CVE-2026-27840? 10 open source packages ship an affected version, including github.com/zitadel/zitadel. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `github.com/zitadel/zitadel` | Go | All versions | None | | `github.com/zitadel/zitadel` | Go | All versions | 1.80.0-v2.20.0.20260216092519-feab8e1fa371 | | `github.com/zitadel/zitadel` | Go | All versions | 1.80.0-v2.20.0.20260216092519-feab8e1fa371 | | `github.com/zitadel/zitadel` | Go | All versions | 1.80.0-v2.20.0.20260216092519-feab8e1fa371 | | `github.com/zitadel/zitadel` | Go | From 2.31.0 to 2.71.19 | None | | `github.com/zitadel/zitadel` | Go | From 2.31.0 to 2.71.19 | None | | `github.com/zitadel/zitadel` | Go | From 3.0.0 | 3.4.7 | | `github.com/zitadel/zitadel` | Go | From 3.0.0 | 3.4.7 | | `github.com/zitadel/zitadel` | Go | From 4.0.0 | 4.11.0 | | `github.com/zitadel/zitadel` | Go | From 4.0.0 | 4.11.0 | Products: Zitadel Zitadel. ## How do I fix CVE-2026-27840? Upgrade github.com/zitadel/zitadel to a fixed version for your release line: 1.80.0-v2.20.0.20260216092519-feab8e1fa371, 3.4.7 or 4.11.0. ## Is CVE-2026-27840 being exploited? There is no known exploitation of CVE-2026-27840 in the wild and no public exploit code. ## Other vulnerabilities in zitadel - [CVE-2026-29191](https://insights.sbomify.com/CVE-2026-29191/): ZITADEL: 1-Click Account Takeover via XSS in /saml-post Endpoint (critical 9.3) - [CVE-2025-67494](https://insights.sbomify.com/CVE-2025-67494/): ZITADEL Vulnerable to Unauthenticated Full-Read SSRF via V2 Login (critical 9.3) - [CVE-2025-27507](https://insights.sbomify.com/CVE-2025-27507/): IDOR Vulnerabilities in ZITADEL's Admin API that Primarily Impact LDAP Configurations (critical 9.0) - [CVE-2025-64103](https://insights.sbomify.com/CVE-2025-64103/): Zitadel Bypass Second Authentication Factor (high 8.7) - [CVE-2025-31123](https://insights.sbomify.com/CVE-2025-31123/): Zitadel Expired JWT Keys Usable for Authorization Grants (high 8.7) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-27840 and fix it if it is affected. What it is: CVE-2026-27840 is a medium-severity authentication bypass vulnerability in zitadel, published on 26 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link. Exploitation: There is no known exploitation of CVE-2026-27840 in the wild and no public exploit code. Affected packages and fixed versions: - github.com/zitadel/zitadel (Go): affected all versions; no fix listed - github.com/zitadel/zitadel (Go): affected all versions; fixed in 1.80.0-v2.20.0.20260216092519-feab8e1fa371 - github.com/zitadel/zitadel (Go): affected all versions; fixed in 1.80.0-v2.20.0.20260216092519-feab8e1fa371 - github.com/zitadel/zitadel (Go): affected all versions; fixed in 1.80.0-v2.20.0.20260216092519-feab8e1fa371 - github.com/zitadel/zitadel (Go): affected from 2.31.0 up to 2.71.19; no fix listed - github.com/zitadel/zitadel (Go): affected from 2.31.0 up to 2.71.19; no fix listed - github.com/zitadel/zitadel (Go): affected from 3.0.0; fixed in 3.4.7 - github.com/zitadel/zitadel (Go): affected from 3.0.0; fixed in 3.4.7 - github.com/zitadel/zitadel (Go): affected from 4.0.0; fixed in 4.11.0 - github.com/zitadel/zitadel (Go): affected from 4.0.0; fixed in 4.11.0 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-27840/ (Markdown: https://insights.sbomify.com/CVE-2026-27840/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27840 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27840 - OSV: https://osv.dev/vulnerability/CVE-2026-27840 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-27840/ Summaries are generated and may contain mistakes; the official description above is the record.