CVE-2026-33523: HTTP response splitting vulnerability in multiple Apache HTTP Server modules with untrusted or compromised bac

This month

MEDIUM 6.5REMOTEWATCHLISTUPGRADE

CVE-2026-33523 is a medium-severity flaw (CVSS 6.5) affecting http server. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 62%)
CISA exploited list	No
Weakness	CWE-443
Published	2026-05-04
Last modified	2026-10-26

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-04 15:16 UTCPublished CVE record published
2026-10-26 19:10 UTCUpdated Record last modified

apache http server UPGRADE

Affected: >= 2.4.0 and < 2.4.67

Fixed in: 2.4.67

Safe to downgrade to: a release before 2.4.0

1. Check installed version

apt-cache policy http-server || rpm -q http-server || http-server --version

2. UPGRADE to 2.4.67 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade http-server

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade http-server

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 2.4.0 (Debian / Ubuntu)

apt-cache madison http-server sudo apt install http-server=<VERSION_BEFORE_2.4.0> sudo apt-mark hold http-server

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list http-server sudo dnf downgrade http-server-<VERSION_BEFORE_2.4.0> sudo dnf versionlock add http-server

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33523?

http server: upgrade to 2.4.67. Exact commands for each OS are on this page.

Is CVE-2026-33523 being exploited?

CVE-2026-33523 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33523 affect?

CVE-2026-33523 affects http server. Severity is medium (CVSS 6.5). 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, wh

How urgent is CVE-2026-33523?

Priority 42/100. Remotely exploitable, no login, no user action; On your watchlist

Software pages

Apache HTTP Server vulnerabilities

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References

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