# Keycloak has authentication bypass via jwt algorithm confusion

Advisory record · `GHSA-j97h-3f8r-mrjr`

- **Identifiers:** `GHSA-j97h-3f8r-mrjr` · `BIT-keycloak-2026-11800` · `CVE-2026-11800`
- **State:** Confirmed
- **Severity:** CVSS 8.1 High
- **Critical:** No
- **Weakness (CWE):** [CWE-347](https://cwe.mitre.org/data/definitions/347.html)
- **Tags:** [Weak cryptography or TLS](https://agentprime.io/advisories/tag/weak-crypto.md)
- **Published:** 3 Nov 2026
- **Updated:** 3 Nov 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 3 Nov 2026, 17:24 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `org.keycloak:keycloak-services` (Maven): affected `<26.6.4`; fixed in `26.6.4`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 8.1 High, CVSS 3.1: `CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N`, from CNA (redhat)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0030, the 22nd percentile, on 5 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 3 Nov 2026, 17:24 UTC: [Confirmed by GitHub Advisory Database](https://github.com/advisories/GHSA-j97h-3f8r-mrjr)
- 3 Nov 2026, 17:45 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-j97h-3f8r-mrjr)

## Sources

- [GitHub Advisory Database: GHSA-j97h-3f8r-mrjr](https://github.com/advisories/GHSA-j97h-3f8r-mrjr)
- [OSV: GHSA-j97h-3f8r-mrjr](https://osv.dev/vulnerability/GHSA-j97h-3f8r-mrjr)
- <https://github.com/keycloak/keycloak/security/advisories/GHSA-j97h-3f8r-mrjr>
- <https://nvd.nist.gov/vuln/detail/CVE-2026-11800>
- <https://github.com/keycloak/keycloak/issues/50357>
- <https://github.com/keycloak/keycloak/pull/50374>
- <https://github.com/keycloak/keycloak/commit/6d61885f20ac59a2ff8b823fc9ed1f1ef1019951>
- <https://github.com/keycloak/keycloak/commit/d343c7373dcc7bfeb9dc14de2309836299c81837>
- <https://access.redhat.com/errata/RHSA-2026:30083>
- <https://access.redhat.com/errata/RHSA-2026:30084>
- <https://access.redhat.com/security/cve/CVE-2026-11800>
- <https://bugzilla.redhat.com/show_bug.cgi?id=2487006>
- <https://github.com/keycloak/keycloak>
- <https://github.com/keycloak/keycloak/releases/tag/26.6.4>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-j97h-3f8r-mrjr>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-j97h-3f8r-mrjr/>. Everything for agents: <https://agentprime.io/llms.txt>.