high CVSS 7.5

CVE-2025-49630·Apache vulnerability

In certain proxy configurations, a denial of service attack against Apache HTTP Server versions 2.4.26 through to 2.4.63 can be triggered by untrusted clients causing an assertion in mod_proxy_http2. Configurations affected are a reverse proxy is configured for an HTTP/2 backend, with ProxyPreserveHost set to "on".

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

Affected versions

From: 2.4.26

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 the assertion failure in mod_proxy_http2. This vulnerability specifically affects reverse proxy configurations with HTTP/2 backends and ProxyPreserveHost enabled, making it critical to update if your deployment matches this setup. Apply the update during a maintenance window and restart the Apache service to ensure the fix is active.

sudo dnf update httpd && sudo systemctl restart httpd

Defensia detects this vulnerability

What an exploitation attempt looks like

Sample log line indicative of exploitation attempts:

GET|POST|HEAD|OPTIONS|CONNECT|TRACE|DELETE|PUT|PATCH requests originating from untrusted networks to a reverse proxy endpoint followed by Apache error log entries containing 'mod_proxy_http2', 'Assertion', or 'core:notice', with corresponding process termination (exit code 134 or 139)

WAF mitigation (if patching is not yet possible)

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

Configure rate limiting and connection limits on reverse proxy endpoints to reduce the impact of DoS attempts. Block or throttle requests from sources sending malformed HTTP/2 frames. Implement request timeout policies to prevent slowdown attacks. However, WAF rules cannot fully prevent this assertion-level vulnerability; upgrading Apache is mandatory.

How to check if you are affected

  1. Run 'apache2ctl -v' or 'httpd -v' to check the installed Apache version; versions 2.4.26 through 2.4.63 are vulnerable
  2. Check your Apache configuration file (typically /etc/apache2/sites-enabled/*.conf or /etc/httpd/conf.d/*.conf) for ProxyPreserveHost On combined with ProxyPass directives pointing to HTTP/2 backends
  3. Search Apache error logs (/var/log/apache2/error.log or /var/log/httpd/error_log) for assertion failures or segmentation faults from mod_proxy_http2 with patterns like 'Assertion.*failed' or 'SIGABRT'
  4. Verify the patch was applied by re-running 'apache2ctl -v' or 'httpd -v' and confirming the version is 2.4.64 or later, then check 'systemctl status apache2' or 'systemctl status httpd' shows the service is running

FAQ

What is CVE-2025-49630?

CVE-2025-49630 is a denial-of-service vulnerability in Apache HTTP Server's mod_proxy_http2 module that triggers an assertion failure when processing certain requests in reverse proxy configurations with HTTP/2 backends and ProxyPreserveHost enabled. Untrusted clients can exploit this to crash the Apache process.

Is CVE-2025-49630 being actively exploited?

No, CVE-2025-49630 is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are currently available. However, the attack requirements are low (network-accessible, no authentication needed), so timely patching is still strongly recommended.

What versions of Apache are affected by CVE-2025-49630?

Apache HTTP Server versions 2.4.26 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-2025-49630?

Run 'apache2ctl -v' or 'httpd -v' to see your version; if it reports 2.4.26–2.4.63, you are vulnerable. Additionally, confirm your Apache config includes 'ProxyPreserveHost On' and at least one 'ProxyPass' directive pointing to an HTTP/2 backend using 'h2://' or 'h2c://' URIs.

Does Defensia detect CVE-2025-49630?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Apache is installed on a monitored server, CVE-2025-49630 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

Track CVEs across your fleet automatically

Defensia scans your Linux servers and tells you exactly which ones are running vulnerable versions — including CVE-2025-49630. Free for 1 server.

Get started free