An HTTP Request Smuggling vulnerability (CWE-444) exists in Pingora's handling of HTTP/1.0 requests and Transfer‑Encoding headers. By exploiting the parser’s acceptance of close‑delimited HTTP/1.0 bodies and its improper treatment of multiple Transfer‑Encoding values, an attacker can craft requests that desynchronize Pingora’s framing from the backend. This flaw allows the attacker to bypass proxy‑level ACLs and WAF logic, poison upstream caches and connections, and perform cross‑user attacks that misuse the trusted proxy IP to hijack sessions or inject requests that appear to originate from the proxy. The impact is a compromise of confidentiality, integrity, and availability of the backends serviced by Pingora.

The flaw affects standalone Pingora instances deployed in front of backends that accept HTTP/1.0 requests. Cloudflare’s own CDN ingress layers were not affected because they exposed only HTTP/1.1 traffic and rejected ambiguous framing. Attackers would require direct access to a vulnerable Pingora deployment or to a backend that accepts HTTP/1.0.

The vulnerability carries a CVSS base score of 9.3, indicating critical severity. The EPSS score is reported as less than 1%, suggesting a low current exploitation probability, and the issue is not listed in the CISA KEV catalog. Nevertheless, the attack vector is remote and straightforward: an attacker sends a crafted HTTP/1.0 or multi‑Transfer‑Encoding request to the Pingora proxy. If the proxy forwards the request, the attacker can bypass controls, cache poisoning, or session hijacking, depending on the backend configuration.