CVE-2026-11800

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.

CVSS v3.1 Score

8.1

HIGH

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

EPSS — Exploit Prediction

0.0018

Probability of exploitation

0.08%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-347 CWE-347

Affected Products

Vendor	Product	Versions
redhat	build_of_keycloak	26.6 — 26.6.4

References

Advisories & Patches

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://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://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-11800.json

Frequently Asked Questions

What is CVE-2026-11800? +

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. It has a CVSS v3.1 base score of 8.1 (HIGH).

How severe is CVE-2026-11800? +

CVE-2026-11800 has a CVSS v3.1 score of 8.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching. The EPSS score is 0.0018, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-11800? +

CVE-2026-11800 affects products from redhat, specifically: build_of_keycloak. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-11800? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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