5.3

CVE-2026-9803: redhat build_of_keycloak Out-of-bounds Read

CVSS: 5.3v3.1MediumModified
AliasesCGA-4f39-42w7-4m4qCGA-68ww-8h67-mvh8CGA-f3mx-77gr-84vp
Published 28-05-2026Last modified 26-06-2026
Open JSON

Vulnerability summary

CVE-2026-9803 is a medium (CVSS 5.3) Out-of-bounds Read vulnerability in redhat build_of_keycloak. EPSS estimates a 0.72% chance of exploitation in the next 30 days, higher than 53.2% of scored vulnerabilities.

Overall risk
21/100
0100
Low · default modelHow is this calculated?
CVSS score
5.3/10
010
Medium · v3.1 (CVE.org)
EPSS score
0.72%
0%100%
Low · +0.30 pp in 30 days
KEVNot listedIn no KEV catalog
RansomwareNone recordedNo known use recorded
Public exploits0No public exploits recorded

Timeline

  1. 28-05-2026
    PublishedVulnerability first disclosed.
  2. 26-06-2026
    Last modifiedVulnerability information updated.

Description

A flaw was found in Keycloak's ClientRegistrationAuth component. A remote unauthenticated attacker can exploit this vulnerability by sending a specially crafted POST request with a malformed 'Authorization: Bearer' header to any client registration endpoint. This can lead to an ArrayIndexOutOfBoundsException, causing the server to return an HTTP 500 error and resulting in a Denial of Service (DoS) for the affected service.

CVSS metrics

5 scores · 5 sources · 1 version

EPSS trend

Probability

0.72%

Chance of exploitation in the next 30 days

Percentile

53%

Versus all other CVEs

30-day change

+0.30 pp

From 0.42% on 21-09-2026

21-09-202621-10-2026
EPSS score
0.72%

Known exploited

Compare KEV catalogs

Not in any of the 3 tracked catalogs.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Chainguard12 products
  • keycloak-26.4All versions (No fix recorded)
  • keycloak-26.4-iamguarded-compatAll versions (No fix recorded)
  • keycloak-26.5All versions (No fix recorded)
  • keycloak-26.5-iamguarded-compatAll versions (No fix recorded)
  • keycloak-fips-26.4All versions (No fix recorded)
Wolfi4 products
  • keycloak-26.4All versions (No fix recorded)
  • keycloak-26.4-iamguarded-compatAll versions (No fix recorded)
  • keycloak-26.5All versions (No fix recorded)
  • keycloak-26.5-iamguarded-compatAll versions (No fix recorded)
Org.keycloak1 product
  • keycloak-services≤ 26.4.7 | ≥ 26.5.0, < 26.6.3
Redhat1 product

4 vendors · 18 products

References

15 links
Show all 15 references