HTTP Response Splitting Vulnerability in Apache HTTP Server - CVE-2026-33523

apache2 Updated 05 May 2026

Summary

04/05/2026

Disclosed on

N/A

Severity

No i

Fix available

Medium

Severity

6.5

CVSS Score

DEBIAN-CVE-2026-33523: HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised backend servers. Affects apache2 versions 2.4.48-3.1 – 2.4.66-8. No fix is published. How to fix ↓

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Background

Apache HTTP Server is a widely used open-source web server software that enables users to serve web content. It is known for its flexibility, performance, and security features. However, certain modules within Apache HTTP Server are vulnerable to HTTP response splitting when interacting with untrusted or compromised backend servers. This vulnerability can lead to various security issues, including cache poisoning and cross-site scripting (XSS).

Vulnerability Detail

The vulnerability identified as CVE-2026-33523 is an HTTP response splitting issue that arises when Apache HTTP Server modules process responses from untrusted or compromised backend servers. This flaw can allow attackers to manipulate HTTP responses, potentially leading to cache poisoning, XSS attacks, and other malicious activities. The vulnerability affects versions of Apache HTTP Server up to 2.4.66, necessitating an upgrade to mitigate the risk.

How To Fix

No fixed version is published for this vulnerability.

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Workaround

As a temporary workaround, users can implement strict validation and sanitization of inputs from backend servers to minimize the risk of HTTP response splitting. However, upgrading to the patched version is the recommended solution.

Conclusion

CVE-2026-33523 represents a significant security risk for users of Apache HTTP Server versions up to 2.4.66. It is crucial for users to upgrade to version 2.4.67 or later to mitigate this vulnerability effectively. Regular monitoring and vulnerability management practices, such as using tools like Vulert, can help maintain the security of open-source software.

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