CVE-2026-88008
Received Received - Intake

HTTP/2 Connection Header Bypass in Traefik

Publication date: 2026-09-10

Last updated on: 2026-09-10

Assigner: GitHub, Inc.

Description
Traefik is an open source HTTP reverse proxy and load balancer. From 2.11.26 until 2.11.57 and 3.7.13, Traefik forwards a client-supplied Connection header requesting Upgrade, the Upgrade: h2c token, and HTTP2-Settings to a shared backend. If the backend accepts h2c and returns 101 Switching Protocols, Traefik enters a raw tunnel and no longer applies routers, BasicAuth, ForwardAuth, IPAllowList, RateLimit, access logging, metrics, or tracing to later HTTP/2 requests, allowing an unauthenticated request through an unprotected route to reach protected paths on the same backend. This issue is fixed in 2.11.57 and 3.7.13.

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Meta Information

Published
2026-09-10
Last Modified
2026-09-10
Generated
2026-09-10
AI Q&A
2026-09-10
EPSS Evaluated
N/A
NVD
CVE-2026-88008
EUVD
EUVD-2026-75545

Affected Vendors & Products

Showing 6 associated CPEs
Vendor Product Version / Range
traefik traefik 2.11.26
traefik traefik From 3.4.2 (inc) to 3.7.13 (exc)
traefik traefik From 2.11.26 (inc) to 2.11.57 (exc)
traefik traefik From 2.11.26 (inc) to 2.11.57 (inc)
traefik traefik 2.11.57
traefik traefik 3.7.13

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-863 The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
CWE-444 The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.

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Executive Summary

This vulnerability in Traefik allows an attacker to bypass security controls by sending a client-supplied HTTP/2 upgrade header (h2c) to a backend server. If the backend accepts the upgrade and responds with a 101 status code, Traefik switches the connection into a raw tunnel, bypassing its security features like authentication, rate limiting, and logging.

Detection Guidance

To detect this vulnerability, check if your Traefik version is between 2.11.26-2.11.57 or 3.7.13 and below. Inspect network traffic for forwarded 'Upgrade: h2c' or 'HTTP2-Settings' headers. Use tools like Wireshark or tcpdump to monitor for raw tunnel connections or unexpected 101 Switching Protocols responses from backends.

Impact Analysis

An attacker could exploit this to send unauthenticated HTTP/2 requests through an unprotected route to reach protected paths on the same backend. This bypasses security controls, allowing unauthorized access to sensitive data or systems. The attack requires a backend that supports h2c upgrades and returns a 101 response.

Compliance Impact

This vulnerability could lead to unauthorized access to protected data, violating compliance requirements for data protection and access control. GDPR and HIPAA mandate strict access controls and logging; bypassing these controls may result in non-compliance, potential data breaches, and legal penalties.

Mitigation Strategies

Upgrade Traefik to versions 2.11.57 or later, or 3.7.13 or later. Disable forwarding of 'Upgrade: h2c' and 'HTTP2-Settings' headers if custom configurations exist. Ensure backends do not accept h2c upgrades unless explicitly required. Monitor for unauthorized tunnel connections or bypassed security controls.

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