CVE-2026-33523: http server — Fix

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.

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CVSS v3.1 Score

6.5

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS — Exploit Prediction

0.0026

Probability of exploitation

0.49%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-443 CWE-443

Affected Products

Vendor	Product	Versions
apache	http_server	2.4.0 — 2.4.67

References

Advisories & Patches

https://httpd.apache.org/security/vulnerabilities_24.html

Other References

http://www.openwall.com/lists/oss-security/2026/05/04/23

Frequently Asked Questions

What is CVE-2026-33523? +

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. It has a CVSS v3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-33523? +

CVE-2026-33523 has a CVSS v3.1 score of 6.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0026, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-33523? +

CVE-2026-33523 affects products from apache, specifically: http_server. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-33523? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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