9.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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CVE-2026-2833

CVE-2026-2833: HTTP Request Smuggling via Premature Upgrade

An HTTP request smuggling vulnerability (CWE-444) was found in Pingora's handling of HTTP/1.1 connection upgrades. The issue occurs when a Pingora proxy reads a request containing an Upgrade header, causing the proxy to pass through the rest of the bytes on the connection to a backend before the backend has accepted the upgrade. An attacker can thus directly forward a malicious payload after a request with an Upgrade header to that backend in a way that may be interpreted as a subsequent request header, bypassing proxy-level security controls and enabling cross-user session hijacking.

Impact

This vulnerability primarily affects standalone Pingora deployments where a Pingora proxy is exposed to external traffic. An attacker could exploit this to:

Bypass proxy-level ACL controls and WAF logic
Poison caches and upstream connections, causing subsequent requests from legitimate users to receive responses intended for smuggled requests
Perform cross-user attacks by hijacking sessions or smuggling requests that appear to originate from the trusted proxy IP

Cloudflare's CDN infrastructure was not affected by this vulnerability, as ingress proxies in the CDN stack maintain proper HTTP parsing boundaries and do not prematurely switch to upgraded connection forwarding mode.

Mitigation:

Pingora users should upgrade to Pingora v0.8.0 or higher

As a workaround, users may return an error on requests with the Upgrade header present in their request filter logic in order to stop processing bytes beyond the request header and disable downstream connection reuse.

(GitHub Advisory)

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CVE-2026-2833

CVE-2026-2833:

9.3

CVSS Score

4.0

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
pingora-core	rust	<= 0.7.0	0.8.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability, CVE-2026-2833, is a classic case of HTTP Request Smuggling due to the premature handling of an HTTP Upgrade. In vulnerable versions of Pingora, when the proxy received a request containing an Upgrade header, it would immediately switch both its client-facing and backend-facing connections into a pass-through or "tunnel" mode. This switch occurred before the backend server had a chance to respond to and approve the upgrade request with a 101 Switching Protocols status code.

The root cause lies in the init_req_body_writer function for the upstream (client) session and the init_body_reader function for the downstream (server) session. Both functions incorrectly assumed that any request with an Upgrade header would successfully be upgraded, and therefore switched the connection to a raw data forwarding mode. An attacker could exploit this by sending a specially crafted request that included an Upgrade header, followed by a second, complete HTTP request in its body. Pingora's proxy logic would only process the first request's headers, apply security policies to it, and then forward it. Because the connection was already in pass-through mode, the second, smuggled request in the body would be sent directly to the backend server as raw data. The backend server, which is not in an upgraded state, would then see and process this as a legitimate, separate HTTP request, bypassing all of Pingora's proxy-level security controls like access control lists (ACLs) and Web Application Firewall (WAF) rules.

The patch corrects this behavior by delaying the switch to the pass-through mode until after the proxy receives a 101 Switching Protocols response from the backend, ensuring that smuggled requests are not forwarded.

Vulnerable functions

pingora_core::protocols::http::v1::client::HttpSession::init_req_body_writer

pingora-core/src/protocols/http/v1/client.rs

This function was responsible for initializing the request body writer for the upstream connection (to the backend). Before the patch, it would immediately switch the body writer to a pass-through mode (`init_http10`) if the incoming request contained an `Upgrade` header. This caused the proxy to forward any subsequent data in the request body as raw bytes to the backend, without waiting for the backend to approve the upgrade. This allowed an attacker to smuggle a second, malicious HTTP request in the body of the initial `Upgrade` request.

pingora_core::protocols::http::v1::server::HttpSession::init_body_reader

pingora-core/src/protocols/http/v1/server.rs

This function was responsible for initializing the request body reader for the downstream connection (from the client). Similar to the client-side counterpart, this function would prematurely switch the body reader to a pass-through mode (`init_http10`) upon seeing an `Upgrade` header in the client's request. This meant that Pingora would stop parsing the incoming byte stream for HTTP request boundaries and instead treat everything after the headers of the `Upgrade` request as a raw payload. This behavior allowed an attacker's smuggled request to be accepted and subsequently forwarded to the backend.

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WAF Rule

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Reasoning

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