Apache HTTP Server: multiple modules: HTTP response splitting forwarding malicious status line

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Summary

CVECVE-2026-33523
StatePUBLISHED
Assignerapache
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-04 15:16:04 UTC
Updated2026-05-04 20:21:15 UTC
DescriptionHTTP 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.

Risk And Classification

Primary CVSS: v3.1 6.5 MEDIUM from ADP

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

Problem Types: CWE-443 | NVD-CWE-Other | CWE-443 CWE-443: HTTP response splitting

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary6.5MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
None

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

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Application Apache Http Server All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Apache Software Foundation Apache HTTP Server affected 2.4.0 2.4.66 semver Not specified

References

ReferenceSourceLinkTags
httpd.apache.org/security/vulnerabilities_24.html [email protected] httpd.apache.org Vendor Advisory
www.openwall.com/lists/oss-security/2026/05/04/23 af854a3a-2127-422b-91ae-364da2661108 www.openwall.com Mailing List, Third Party Advisory
CVE Program record CVE.ORG www.cve.org canonical
NVD vulnerability detail NVD nvd.nist.gov canonical, analysis

Vendor Comments And Credit

Discovery Credit

CNA: Haruki Oyama (Waseda University) (en)

CNA: Merih Mengisteab (en)

CNA: Dawit Jeong (en)

Additional Advisory Data

SourceTimeEvent
CNA2026-03-05T12:00:00.000Zreported
CNA2026-05-04T12:00:00.000Z2.4.67 released
CNA2026-05-04T12:00:00.000Zfixed in 2.4.x by r1933360
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