SB2026091073 - Multiple vulnerabilities in Keycloak
Published: September 10, 2026
Breakdown by Severity
- Low
- Medium
- High
- Critical
Description
This security bulletin contains information about 3 vulnerabilities.
1) Allocation of Resources Without Limits or Throttling (CVE-ID: CVE-2026-33871)
CWE-ID: CWE-770 - Allocation of Resources Without Limits or Throttling
CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to perform a denial of service (DoS) attack.
The vulnerability exists due to allocation of resources without limits or throttling in the "DefaultHttp2FrameReader" function within HTTP/2 server. A remote attacker can send a flood of CONTINUATION frames and cause a denial of service condition on the target system.
2) Inconsistent interpretation of HTTP requests (CVE-ID: CVE-2026-33870)
CWE-ID: CWE-444 - Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling')
CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to perform HTTP request smuggling attacks.
The vulnerability exists due to improper validation of HTTP requests within chunked transfer encoding extension values. A remote attacker can send a specially crafted HTTP request to the server and smuggle arbitrary HTTP headers.
3) Use of a broken or risky cryptographic algorithm (CVE-ID: CVE-2026-5588)
CWE-ID: CWE-327 - Use of a Broken or Risky Cryptographic Algorithm
CVSSv4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
The vulnerability allows a remote attacker to bypass signature verification.
The vulnerability exists due to use of a broken or risky cryptographic algorithm in the PKIX draft CompositeVerifier when processing composite signatures. A remote attacker can provide an empty signature sequence to bypass signature verification.
Remediation
Install update from vendor's website.