What is CVE-2026-33523?

CVE-2026-33523 is a medium-severity vulnerability in Apache HTTP Server, classified under CWE-443. CVSS score: 6.5/10. Published 2026-05-04.

How severe is CVE-2026-33523?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Vulnerability in Apache HTTP Server

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.

Published 2026-05-04 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.010 (62.7th percentile), scored 2026-09-30.

Low probability of exploitation in the next 30 days, but still tracked. 63rd percentile — 62.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.010 · change: +0.006

Affected products

Apache HTTP Server
Apache Software Foundation HTTP Server — versions 2.4.0

Weakness classification (CWE)

CWE-443

References

httpd.apache.org/security/vulnerabilities_24.html (vendor-advisory, Vendor Advisory)
af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2026-33523?: CVE-2026-33523 is a medium-severity vulnerability in Apache HTTP Server, classified under CWE-443. CVSS score: 6.5/10. Published 2026-05-04.
How severe is CVE-2026-33523?: Medium severity. CVSS v3 base score is 6.5 out of 10.