Vulnerability · Published May 4, 2026 · Assigned by apache
CVE-2026-33523Apache HTTP Server: multiple modules: HTTP response splitting forwarding malicious status line
Medium 6.5
In plain English
A medium-severity security flaw in Apache HTTP Server from Apache Software Foundation. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 38% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Severity (CVSS 3.1)6.5Medium
Exploit odds (30 days)0.4%top 61.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers. This issue affects Apache HTTP Server: from through 2.4.66. Users are recommended to upgrade to version 2.4.67, which fixes the issue.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine:v3.20 | apache2 | 2.4.67-r0 | ALPINE-CVE-2026-33523 |
| Alpine:v3.21 | apache2 | 2.4.67-r0 | ALPINE-CVE-2026-33523 |
| Alpine:v3.22 | apache2 | 2.4.67-r0 | ALPINE-CVE-2026-33523 |
| Alpine:v3.23 | apache2 | 2.4.67-r0 | ALPINE-CVE-2026-33523 |
| Alpine:v3.24 | apache2 | 2.4.67-r0 | ALPINE-CVE-2026-33523 |
| Debian:12 | apache2 | 2.4.67-1~deb12u2 | DEBIAN-CVE-2026-33523 |
| Debian:13 | apache2 | 2.4.67-1~deb13u2 | DEBIAN-CVE-2026-33523 |
| Debian:14 | apache2 | 2.4.67-1 | DEBIAN-CVE-2026-33523 |
| Ubuntu:22.04:LTS | apache2 | 2.4.52-1ubuntu4.20 | UBUNTU-CVE-2026-33523 |
| Ubuntu:24.04:LTS | apache2 | 2.4.58-1ubuntu8.12 | UBUNTU-CVE-2026-33523 |
| Ubuntu:25.10 | apache2 | 2.4.64-1ubuntu3.4 | UBUNTU-CVE-2026-33523 |
| Ubuntu:26.04:LTS | apache2 | 2.4.66-2ubuntu2.1 | UBUNTU-CVE-2026-33523 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| Apache Software Foundation | Apache HTTP Server | 2.4.0 – through 2.4.66 |
Weakness: CWE-443 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N