CVE-2026-33523 | Apache HTTP Server: multiple modules: HTTP response splitting forwarding malicious status line

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 update: 2026-05-04 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-33523 is rated Moderate Risk (43.4/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.26%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-33523

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-22 0.16% 0.26% +0.09%
2 2026-05-05 — 0.16% —

Full EPSS history (2 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-33523

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 2.5 134c704f-9b21-4f2e-91b3-4a467353bcc0

Weakness enumeration for CVE-2026-33523

GitHub Security Advisory for CVE-2026-33523

GHSA-fc75-39v4-qm5p · Severity: medium — HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or...

OS Trackers for CVE-2026-33523

vendor priority summary link
debian not yet assigned CVE-2026-33523 not yet assigned priority: Debian including 1 source packages (apache2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-33523
suse high — https://www.suse.com/security/cve/CVE-2026-33523/
ubuntu low CVE-2026-33523 low priority: Ubuntu including 1 source packages (apache2), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): released 5, needs-triage 4. https://ubuntu.com/security/CVE-2026-33523

Affected software / configurations for CVE-2026-33523

Vendor Product Version Raw CPE
apache http_server >= 2.4.0, < 2.4.67 cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*

References for CVE-2026-33523

cvelogic Threat Intelligence