CVE-2026-63718: 
Apache HTTP Server vulnerability analysis and mitigation

CVE-2026-63718 is an HTTP Request/Response Smuggling vulnerability in Apache HTTP Server affecting the mod_proxy_uwsgi module. It arises when the server processes a crafted uwsgi response containing a malicious Transfer-Encoding header, leading to inconsistent HTTP request interpretation (CWE-444). The vulnerability affects Apache HTTP Server versions 2.4.30 through 2.4.68 and was disclosed on October 1, 2026. It carries a CVSS v3.1 base score of 7.5 (High) (GitHub Advisory, Apache Advisory).

The root cause is classified as CWE-444 (Inconsistent Interpretation of HTTP Requests / HTTP Request Smuggling), mapped to CAPEC-33. When Apache HTTP Server acts as a reverse proxy via mod_proxy_uwsgi, it fails to consistently interpret Transfer-Encoding headers in crafted uwsgi backend responses. An unauthenticated remote attacker can exploit this by sending a specially crafted uwsgi response that causes the proxy to misparse HTTP message boundaries, enabling injection of smuggled HTTP requests into the pipeline. No preconditions beyond the target running a vulnerable version of Apache with mod_proxy_uwsgi enabled are required, and exploitation is considered automatable (GitHub Advisory, Apache Advisory).

Successful exploitation primarily affects integrity (CVSS integrity impact: High), with no direct confidentiality or availability impact per the CVSS scoring. An attacker can inject smuggled HTTP requests that bypass security controls such as WAFs or authentication layers, poison shared caches to serve malicious content to other users, or manipulate downstream request handling in ways that could facilitate further attacks. The attack is network-based and requires no authentication or user interaction, making it broadly exploitable against any deployment using mod_proxy_uwsgi (GitHub Advisory).

As of the disclosure date (October 1, 2026), there is no known public proof-of-concept exploit and no evidence of in-the-wild exploitation. The NVD SSVC assessment classifies exploitation as "none" at this time, though the attack is rated as automatable. The EPSS score is 0.0, and the vulnerability has not been added to the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported (GitHub Advisory, Apache Advisory).

Apache has released a patch addressing this vulnerability; administrators should upgrade Apache HTTP Server to a version beyond 2.4.68 as soon as it becomes available. As an interim workaround, organizations that do not require uwsgi proxying should disable mod_proxy_uwsgi entirely. Additionally, deploying strict HTTP request/response validation and filtering at network boundaries — specifically inspecting and blocking responses with suspicious or conflicting Transfer-Encoding headers — can reduce exposure. Monitoring proxy traffic for anomalous HTTP message framing is also recommended (GitHub Advisory, Apache Advisory).

The vulnerability was noted on Bluesky by the infosec community shortly after disclosure, and was picked up by standard vulnerability tracking platforms including VulDB, OSS-Security mailing list, and the Apache announcement list. No major vendor statements or notable researcher deep-dives have been published beyond the initial advisory as of the disclosure date (OSS-Sec List, Apache Announce).