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

mediumCVSS 6.5CVE-2026-33523

CSIRTS triage

vendor: Apache product: HTTP Server Cross-site scripting

What: Multiple Apache HTTP Server modules fail to properly validate HTTP response status lines, allowing malicious status lines to be forwarded and causing HTTP response splitting.
Who is affected: Apache HTTP Server deployments using affected modules.
Urgency: Medium priority; response splitting can lead to cache poisoning or XSS but requires specific module configuration.
Action: Update to the patched Apache HTTP Server version addressing CVE-2026-33523.

AI-assisted analysis generated from the source advisory — verify against the original.

⚡ Watch HTTP Server

Get an email when a new HTTP Server advisory drops — max one per day, one-click unsubscribe.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 6.5
Published: 2026-08-06
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33523

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-335230.44% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 37% of all EPSS-scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-33523	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

high[UPDATE] [high] Apache HTTP Server: Multiple vulnerabilitiescert-bund
unknownMultiple vulnerabilities in Tenable products (August 4, 2026)cert-fr-avis
unknownMultiple vulnerabilities in Tenable Security Center (July 21, 2026)cert-fr-avis
unknownUSN-8571-1: Apache HTTP Server vulnerabilitiesubuntu

Recent advisories for Apache HTTP Server

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

high[UPDATE] [high] Apache HTTP Server: Multiple vulnerabilitiescert-bund · 2026-08-25
highCVE-2026-54789: mod_auth_openidc is an OpenID Certified authentication and authorization module for the Apache…nvd · 2026-08-21
high[UPDATE] [high] Apache HTTP Server: Multiple vulnerabilitiescert-bund · 2026-08-21
mediumCVE-2026-63044: Server-Side Request Forgery (SSRF) vulnerability in Apache InLong. Any authenticated user (no …nvd · 2026-08-20
high[UPDATE] [high] Apache HTTP Server: Multiple vulnerabilitiescert-bund · 2026-08-20
medium[UPDATE] [medium] Apache HTTP Server: Multiple Vulnerabilities Allow Data Manipulationcert-bund · 2026-08-20