How severe is CVE-2026-33523?

CVE-2026-33523 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-33523 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33523?

CVE-2026-33523 affects Apache Http Server. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33523?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-33523 have an EU (EUVD) identifier?

Yes. CVE-2026-33523 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-26965.

When was CVE-2026-33523 published?

CVE-2026-33523 was published on 2026-05-04 and last updated on 2026-06-17.

CVE-2026-33523

CVE-2026-33523 is a medium-severity vulnerability in Apache Http Server with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-443.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (35th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-26965
Weakness: CWE-443
Affected product: Apache Http Server
Published: 2026-05-04
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2026-33523?: CVE-2026-33523 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-33523 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (35th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33523?: CVE-2026-33523 affects Apache Http Server. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33523?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-33523 have an EU (EUVD) identifier?: Yes. CVE-2026-33523 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-26965.
When was CVE-2026-33523 published?: CVE-2026-33523 was published on 2026-05-04 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*

More vulnerabilities in Apache Http Server

CVE-2010-0425 — Critical (CVSS 10.0): modules/arch/win32/mod_isapi.c in mod_isapi in the Apache HTTP Server 2.0.37 through 2.0.63, 2.2.0 through 2.2.14, and…
CVE-2005-2700 — Critical (CVSS 10.0): ssl_engine_kernel.c in mod_ssl before 2.8.24, when using "SSLVerifyClient optional" in the global virtual host…
CVE-2004-0492 — Critical (CVSS 10.0): Heap-based buffer overflow in proxy_util.c for mod_proxy in Apache 1.3.25 to 1.3.31 allows remote attackers to cause a…
CVE-2003-0789 — Critical (CVSS 10.0): mod_cgid in Apache before 2.0.48, when using a threaded MPM, does not properly handle CGI redirect paths, which could…
CVE-1999-1293 — Critical (CVSS 10.0): mod_proxy in Apache 1.2.5 and earlier allows remote attackers to cause a denial of service via malformed FTP commands,…
CVE-1999-0926 — Critical (CVSS 10.0): Apache allows remote attackers to conduct a denial of service via a large number of MIME headers.

All CVEs affecting Apache Http Server →

Threat intelligence

Threat-intel indicators referencing this CVE:

37.120.213.13 (ipv4-addr)
50.255.62.89 (ipv4-addr)
147.15.15.226 (ipv4-addr)
45.84.120.3 (ipv4-addr)
77.90.185.88 (ipv4-addr)
77.90.185.87 (ipv4-addr)
74.87.117.150 (ipv4-addr)
61.76.112.4 (ipv4-addr)