CVE-2026-2833

published 2026-03-05

CVE-2026-2833: 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…

Priority P2 61 critical 9.1 CVSS 3.1

AV N AC L PR N UI N S U C H I H A N

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.

Affected

2 ranges

Vendor	Product	Version range	Fixed in
cloudflare	https_github.com_cloudflare_pingora	< 0.8.0	0.8.0
cloudflare	pingora	< 0.8.0	0.8.0

Detection & IOCs extracted from sources · hover to see the quote

• → Detect HTTP requests containing an 'Upgrade' header being forwarded through a Pingora proxy — these are the trigger condition for the smuggling vulnerability and should be flagged or blocked at the proxy request filter stage. ↗
• → Monitor for unexpected or anomalous HTTP requests arriving at backend servers that appear to originate from the trusted proxy IP but contain smuggled request headers — indicative of cross-user session hijacking via HTTP request smuggling. ↗
• → Alert on cache poisoning indicators: legitimate users receiving responses intended for smuggled requests, which may manifest as mismatched session data or unexpected response content in proxy/CDN logs. ↗
• → In Pingora proxy request filter logic, inspect for the presence of the 'Upgrade' header and return an error to prevent downstream connection reuse and stop processing bytes beyond the request header. ↗

• · Only standalone Pingora deployments exposed to external traffic are affected; Cloudflare's own CDN infrastructure was explicitly confirmed not impacted due to proper HTTP parsing boundaries at ingress proxies. ↗
• · Cloudflare CDN infrastructure is not affected and does not require patching or workaround application. ↗
• · The affected component is specifically 'pingora-core'; operators should verify which version of pingora-core is in use and upgrade to Pingora v0.8.0 or higher to remediate. ↗

CVSS provenance

nvd v3.1 9.1 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

nvd v4.0 9.3 CRITICAL CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

ghsa 9.3 CRITICAL

osv 9.3 CRITICAL

Stop checking back — get the weekly exploitation signal.

Every Monday: what got weaponized or added to CISA KEV in the last seven days — each CVE cross-linked to its PoC, Nuclei template, and detection rule. Free, one email a week, unsubscribe in one click.

CWE-444