high CVSS 7.5

CVE-2024-42516·Apache vulnerability

HTTP response splitting in the core of Apache HTTP Server allows an attacker who can manipulate the Content-Type response headers of applications hosted or proxied by the server can split the HTTP response. This vulnerability was described as CVE-2023-38709 but the patch included in Apache HTTP Server 2.4.59 did not address the issue. Users are recommended to upgrade to version 2.4.64, which fixes this issue.

Severity
high
Software
Apache
Fixed in
2.4.64
Published
2025-07-10

Affected versions

From: 2.4.0

Until: 2.4.64

Fixed in: 2.4.64

How to fix this CVE

Upgrade Apache HTTP Server to version 2.4.64 or later to patch a response-splitting vulnerability that could allow attackers to inject malicious HTTP headers. Organizations running versions 2.4.0 through 2.4.63 should prioritize this update, particularly if the server processes user-controlled or application-provided Content-Type headers. This vulnerability was initially addressed in 2.4.59 but the fix was incomplete, making 2.4.64 the first fully patched release.

sudo dnf update httpd

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

POST|GET .* HTTP/1\.1\r\nContent-Type:[^\r]*(%0d|%0a|\r|\n)+[A-Za-z-]+:|^[^\r]*\r\n\r\n[A-Za-z-]+: [^\r]*\r\n

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement a WAF rule to block HTTP requests with CRLF sequences (%0d, %0a, \r, \n) in the Content-Type header or any response header fields. Additionally, reject requests with malformed or duplicate Content-Type headers that could be used to inject response data.

How to check if you are affected

  1. Check installed Apache version: apache2ctl -v (Ubuntu/Debian) or httpd -v (RHEL/CentOS/Amazon Linux)
  2. Verify the server is exposed to untrusted client connections by checking firewall rules and virtual host configurations: grep -r 'VirtualHost' /etc/apache2/sites-enabled/ or /etc/httpd/conf/
  3. Search Apache access and error logs for suspicious Content-Type header patterns or CRLF injection attempts: grep -E '(%0d|%0a|\r|\n)' /var/log/apache2/access.log* or /var/log/httpd/access_log*
  4. Confirm the patched version is running after upgrade: apache2ctl -v or httpd -v (should show 2.4.64 or higher)

FAQ

What is CVE-2024-42516?

CVE-2024-42516 is an HTTP response-splitting vulnerability in Apache HTTP Server that occurs when an attacker manipulates Content-Type response headers to inject additional HTTP headers or split the HTTP response. This can lead to cache poisoning, session hijacking, or cross-site scripting attacks.

Is CVE-2024-42516 being actively exploited?

No, CVE-2024-42516 is not currently listed as actively exploited in the CISA KEV catalog, and no public exploits are documented. However, its high CVSS score of 7.5 and the ease of crafting Content-Type headers make proactive patching essential.

What versions of Apache are affected by CVE-2024-42516?

All versions from Apache HTTP Server 2.4.0 through 2.4.63 are vulnerable. Version 2.4.64 and later contain the fix.

How do I check if my server is vulnerable to CVE-2024-42516?

Run 'httpd -v' or 'apache2ctl -v' to display the installed version. If the output shows version 2.4.0 through 2.4.63, your server is vulnerable and requires immediate upgrade to 2.4.64 or later.

Does Defensia detect CVE-2024-42516?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2024-42516 will appear in your dashboard with remediation steps.

Related Apache CVEs

CVE-2024-38476CVSS 9.8Vulnerability in core of Apache HTTP Server 2.4.59 and earlier are vulnerably to information disclosure, SSRF or local script execution via backend applications whose response headers are malicious or exploitable. Users are recommended to upgrade to version 2.4.60, which fixes this issue.
CVE-2024-38474CVSS 9.8Substitution encoding issue in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows attacker to execute scripts in directories permitted by the configuration but not directly reachable by any URL or source disclosure of scripts meant to only to be executed as CGI. Users are recommended to upgrade to version 2.4.60, which fixes this issue. Some RewriteRules that capture and substitute unsafely will now fail unless rewrite flag "UnsafeAllow3F" is specified.
CVE-2024-38475CVSS 9.1Improper escaping of output in mod_rewrite in Apache HTTP Server 2.4.59 and earlier allows an attacker to map URLs to filesystem locations that are permitted to be served by the server but are not intentionally/directly reachable by any URL, resulting in code execution or source code disclosure. Substitutions in server context that use a backreferences or variables as the first segment of the substitution are affected.  Some unsafe RewiteRules will be broken by this change and the rewrite flag "UnsafePrefixStat" can be used to opt back in once ensuring the substitution is appropriately constrained.
CVE-2025-23048CVSS 9.1In some mod_ssl configurations on Apache HTTP Server 2.4.35 through to 2.4.63, an access control bypass by trusted clients is possible using TLS 1.3 session resumption. Configurations are affected when mod_ssl is configured for multiple virtual hosts, with each restricted to a different set of trusted client certificates (for example with a different SSLCACertificateFile/Path setting). In such a case, a client trusted to access one virtual host may be able to access another virtual host, if SSLStrictSNIVHostCheck is not enabled in either virtual host.
CVE-2025-58098CVSS 8.3Apache HTTP Server 2.4.65 and earlier with Server Side Includes (SSI) enabled and mod_cgid (but not mod_cgi) passes the shell-escaped query string to #exec cmd="..." directives. This issue affects Apache HTTP Server before 2.4.66. Users are recommended to upgrade to version 2.4.66, which fixes the issue.

References

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