HTTP response splitting in Apache HTTP Server - CVE-2026-33523

Vulnerability identifier: #VU129543

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-33523

CWE-ID: CWE-113

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to manipulate HTTP responses.

The vulnerability exists due to improper neutralization of CRLF sequences in multiple Apache HTTP Server modules when forwarding a backend status line. A remote attacker can supply a malicious backend response to manipulate HTTP responses.

Exploitation requires an untrusted or compromised backend server.

Apache HTTP Server
IBM HTTP Server
Debian Linux
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server 12 SP5
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP5
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing 12
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
Ubuntu
SUSE Package Hub 15
Server Applications Module
Basesystem Module
openSUSE Leap
openEuler
SecurityCenter
WebSphere Remote Server
IBM Rational ClearQuest
IBM Rational ClearCase
IBM Business Automation Workflow
IBM OpenPages with Watson
DevOps Code ClearCase
apache2 (Ubuntu package)
httpd-help
httpd-filesystem
mod_ssl
mod_session
mod_proxy_html
mod_md
mod_ldap
httpd-tools
httpd-devel
httpd-debugsource
httpd-debuginfo
httpd
apache2-example-pages
apache2-tls13-devel
apache2-prefork-debuginfo
apache2-worker
apache2-tls13-prefork-debuginfo
apache2-prefork
apache2-devel
apache2-debugsource
apache2-tls13-worker-debuginfo
apache2-utils-debuginfo
apache2-tls13-example-pages
apache2
apache2-debuginfo
apache2-tls13-worker
apache2-tls13-debugsource
apache2-tls13-debuginfo
apache2-tls13
apache2-tls13-utils-debuginfo
apache2-utils
apache2-tls13-prefork
apache2-tls13-utils
apache2-worker-debuginfo
apache2-doc
apache2-tls13-doc
apache2-event-debuginfo
apache2-event
apache2-utils-debugsource
apache2-worker-debugsource
apache2-event-debugsource
apache2-prefork-debugsource
apache2-manual
apache2 (Debian package)

Install security update from vendor's website.

Apache HTTP Server - update to 2.4.67
SecurityCenter - addressed in versions SC202607.1, SC202607.2
IBM HTTP Server - addressed in versions 8.5.5.30, 9.0.5.28
apache2 (Ubuntu package) - addressed in versions 2.4.7-1ubuntu4.22+esm14, 2.4.18-2ubuntu3.17+esm19, 2.4.29-1ubuntu4.27+esm10, 2.4.41-4ubuntu3.23+esm5, 2.4.52-1ubuntu4.20, 2.4.58-1ubuntu8.12, 2.4.64-1ubuntu3.4, 2.4.66-2ubuntu2.1
httpd-help - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd-filesystem - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
mod_ssl - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
mod_session - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
mod_proxy_html - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
mod_md - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
mod_ldap - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd-tools - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd-devel - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd-debugsource - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd-debuginfo - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
httpd - addressed in versions 2.4.43-35, 2.4.51-30, 2.4.58-15
apache2-example-pages - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1
apache2-tls13-devel - update to 2.4.66-35.78.1
apache2-prefork-debuginfo - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-worker - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-tls13-prefork-debuginfo - update to 2.4.66-35.78.1
apache2-prefork - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-devel - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-debugsource - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-tls13-worker-debuginfo - update to 2.4.66-35.78.1
apache2-utils-debuginfo - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-tls13-example-pages - update to 2.4.66-35.78.1
apache2 - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-debuginfo - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-tls13-worker - update to 2.4.66-35.78.1
apache2-tls13-debugsource - update to 2.4.66-35.78.1
apache2-tls13-debuginfo - update to 2.4.66-35.78.1
apache2-tls13 - update to 2.4.66-35.78.1
apache2-tls13-utils-debuginfo - update to 2.4.66-35.78.1
apache2-utils - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-tls13-prefork - update to 2.4.66-35.78.1
apache2-tls13-utils - update to 2.4.66-35.78.1
apache2-worker-debuginfo - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-doc - addressed in versions 2.4.66-35.78.1, 2.4.66-150400.6.57.1
apache2-tls13-doc - update to 2.4.66-35.78.1
apache2-event-debuginfo - addressed in versions 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-event - addressed in versions 2.4.66-150400.6.57.1, 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-utils-debugsource - addressed in versions 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-worker-debugsource - addressed in versions 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-event-debugsource - addressed in versions 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-prefork-debugsource - addressed in versions 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2-manual - addressed in versions 2.4.66-150600.5.52.1, 2.4.66-150700.4.20.1
apache2 (Debian package) - addressed in versions 2.4.67-1~deb12u2, 2.4.67-1~deb13u2

• https://httpd.apache.org/security/vulnerabilities_24.html#CVE-2026-33523
• https://lists.apache.org/thread/88f06q3opz3snbsfbyj4x6zqrzkklto6

• Multiple vulnerabilities in Apache HTTP Server
• Ubuntu update for apache2
• Multiple vulnerabilities in IBM HTTP Server
• Debian update for apache2
• Multiple vulnerabilities in IBM Business Automation Workflow
• openEuler 24.03 LTS SP1 update for httpd
• Multiple vulnerabilities in IBM WebSphere Remote Server
• Multiple vulnerabilities in IBM DevOps Code ClearCase
• openEuler 22.03 LTS SP4 update for httpd
• openEuler 20.03 LTS SP4 update for httpd
• openEuler 24.03 LTS SP3 update for httpd
• openEuler 24.03 LTS update for httpd
• Multiple vulnerabilities in IBM OpenPages
• SUSE update for apache2
• SUSE update for apache2
• Multiple vulnerabilities in IBM Rational ClearQuest
• SUSE update for apache2
• SUSE update for apache2
• Ubuntu update for apache2
• Multiple vulnerabilities in Tenable Security Center
• Tenable Security Center on Enclave Security update for third-party components