Apache HTTP Server: mod_proxy_http2 denial of service
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".
02 / AFFECTED SOFTWARE
Affected packages
03 / CONNECTIONS
Connected vulnerabilities
04 / EVIDENCE
Source records
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".
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".
05 / REFERENCES
Further evidence
- http://www.openwall.com/lists/oss-security/2025/07/10/2
- http://www.openwall.com/lists/oss-security/2025/07/10/7
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2025/49xxx/CVE-2025-49630.json
- https://httpd.apache.org/security/vulnerabilities_24.html
- https://lists.debian.org/debian-lts-announce/2025/08/msg00009.html
- https://nvd.nist.gov/vuln/detail/CVE-2025-49630