Keycloak vulnerable to infinite loop based Denial of Service

published 2018-07-27 8 y ago modified 2026-06-17 4 mo ago also GHSA-jc6q-27mw-p55w , EUVD-2018-0629

cvss: 7.5; version 3.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 1.8%; EPSS 1.8% chance of exploitation in 30 days, percentile 79%
public exploits: 0; none known

It was found that when Keycloak before 2.5.5 receives a Logout request with a Extensions in the middle of the request, the SAMLSloRequestParser.parse() method ends in a infinite loop. An attacker could use this flaw to conduct denial of service attacks.

Patch / fix

fixed in 2

maven org.keycloak:keycloak-core 2.5.5
redhat keycloak 2.5.5

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2017-2646 updated 2026-06-30 cvss 7.5

keycloak: DoS via SAML request

Red Hat Single Sign-On 7 rh-sso7-keycloak rh-sso7-keycloak
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.83% chance of exploitation in the next 30 days, higher than 79% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.0	7.5	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD	3.0	7.5	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD	2.0	5.0	AV:N/AC:L/Au:N/C:N/I:N/A:P
GitHub	3.0	7.5	CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem	package	affected	fixed in
maven	org.keycloak:keycloak-core	<2.5.5	2.5.5

Affected products

Red Hat keycloak

Classification

Weakness

CWE-835 Loop with Unreachable Exit Condition

References

bugzilla.redhat.com /show_bug.cgi?id=CVE-2017-2646
issue-tracking, third-party-advisory
securityfocus.com /bid/96882
vdb-entry, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2017-2646
advisory
github.com /advisories/GHSA-jc6q-27mw-p55w
advisory
github.com /keycloak/keycloak
package

Sources

CVE List CVE-2017-2646
GitHub Advisory GHSA-jc6q-27mw-p55w
NVD CVE-2017-2646

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary