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Response snapshot Nov 3, 2026, 19:21 UTC

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VulnerabilityCVE-2026-11800

Keycloak has authentication bypass via jwt algorithm confusion

A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens.

At a glance

Exploited
Not known
Severity
8.1 High (CVSS 3.1)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: org.keycloak:keycloak-services: 26.6.4. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-j97h-3f8r-mrjr (opens a new tab)

What happened

Description

A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens. This enables the attacker to impersonate any federated user linked to the affected Identity Provider, leading to unauthorized access and potential privilege escalation.

Affected package ranges reported by GitHub: org.keycloak:keycloak-services: < 26.6.4

Scores and how they were measured

CVSS base severity

8.1

Version 3.1As of

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

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-j97h-3f8r-mrjr (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-j97h-3f8r-mrjr, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 3). Keycloak has authentication bypass via jwt algorithm confusion (CVE-2026-11800). https://kevwire.com/record/CVE-2026-11800

MLA

"Keycloak has authentication bypass via jwt algorithm confusion (CVE-2026-11800)." KEVWire, 3 Nov. 2026, kevwire.com/record/CVE-2026-11800.

Chicago

KEVWire. "Keycloak has authentication bypass via jwt algorithm confusion (CVE-2026-11800)." Last modified November 3, 2026. https://kevwire.com/record/CVE-2026-11800.

Evidence summary (plain text)

Keycloak has authentication bypass via jwt algorithm confusion (Nov 3, 2026).
A flaw was found in Keycloak. This JWT algorithm confusion vulnerability in the JWT Authorization Grant flow allows an attacker with valid client credentials to bypass signature verification. By forging an assertion, the attacker can create unauthorized access tokens. This enables the attacker to impersonate any federated user linked to the affected Identity Provider, leading to unauthorized access and potential privilege escalation.
CVSS 8.1 (version 3.1; evidence as of Nov 3, 2026; https://github.com/advisories/GHSA-j97h-3f8r-mrjr).
Sources:
GitHub-reviewed advisory GHSA-j97h-3f8r-mrjr: https://github.com/advisories/GHSA-j97h-3f8r-mrjr
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-11800.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 3, 2026, 19:00 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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Record details

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