An HTTP request smuggling flaw in Pingora’s handling of HTTP/1.1 connection upgrades allows an attacker to send a request that contains an Upgrade header. The proxy forwards the rest of the received bytes to the backend before the backend has processed the upgrade request, causing the following bytes to be interpreted as a separate HTTP request. This can bypass proxy‑level ACLs, WAF rules, and other security controls, leading to session hijacking, cache poisoning, and cross‑user attacks. The weakness is identified as CWE‑444 and is defined as a high‑severity request smuggling vulnerability.

The vulnerability impacts standalone deployments of Cloudflare Pingora that are exposed directly to external traffic. Users running versions prior to v0.8.0 are affected; all newer releases incorporate the fix. The problem does not affect Cloudflare’s CDN ingress proxies, which enforce proper HTTP parsing boundaries.

The CVSS score of 9.3 signals a critical risk, but the EPSS score of less than 1% indicates that exploitation is currently considered unlikely by industry metrics. The flaw is not listed in CISA’s KEV catalog, suggesting no known active exploitation yet. Because the attack requires crafting a specially formatted HTTP request that includes an Upgrade header, the vector is network‑based; any host reachable over HTTP/1.1 can serve as a target. If an attacker succeeds, the immediate consequence is ability to issue arbitrary requests to backends from the perspective of the trusted proxy, enabling policy bypass and session hijacking.