---
id: "CVE-2026-119574"
kind: "vulnerability"
aliases: ["CVE-2026-119574"]
title: "Traefik: data race in experimental FastProxy lets anyone crash the proxy"
severity: "high"
cvss: 8.2
epss: null
exploited: false
status: "open"
category: "infrastructure"
products: []
ecosystems: []
tags: ["infrastructure", "kubernetes", "self-hosted", "traefik", "websocket"]
not_affected_if: ["default-config", "managed-hosting"]
published_at: "2026-10-30T14:16:46+00:00"
first_seen_at: "2026-10-30T14:30:54+00:00"
updated_at: "2026-10-30T14:32:36+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-119574", "first_seen_at": "2026-10-30T14:30:54+00:00"}]
---

# Traefik: data race in experimental FastProxy lets anyone crash the proxy

Traefik versions from 3.2.0 before 3.7.15 have a data race in the experimental FastProxy feature, where repeatedly opening and aborting HTTP/1 upgraded connections such as WebSocket corrupts a shared buffer. An unauthenticated attacker can trigger an unrecovered panic that terminates the Traefik process.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `traefik version` and check whether it reports a version from `3.2.0` up to but not including `3.7.15`.
- Check the static configuration for the experimental FastProxy setting; the sources do not name the exact key, so treat it as unknown.

## Fix

- Move Traefik to `3.7.15` or later.

## Timeline

- 2026-10-30T14:30:54+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-119574

## From the sources

Traefik from 3.2.0 before 3.7.15 contains a data race in the experimental FastProxy that allows unauthenticated attackers to crash the process by abusing HTTP/1 protocol upgrades. Attackers can repeatedly open and abort upgraded connections such as WebSocket, corrupting the unsynchronized shared bufio.Reader and triggering an unrecovered panic that terminates Traefik.

---

_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_