---
id: "CVE-2025-55702"
kind: "vulnerability"
aliases: ["CVE-2025-55702"]
title: "Apache Traffic Server: Expect 100-continue request smuggling past front-end proxies"
severity: "high"
cvss: 8.7
epss: 0.00253
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["apache-traffic-server", "reverse-proxy", "runtime", "self-hosted"]
not_affected_if: ["default-config"]
published_at: "2026-10-21T19:16:48+00:00"
first_seen_at: "2026-10-23T21:57:29+00:00"
updated_at: "2026-10-24T13:15:54+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2025-55702", "first_seen_at": "2026-10-23T21:57:29+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2025-55702", "first_seen_at": "2026-10-24T13:15:54+00:00"}]
---

# Apache Traffic Server: Expect 100-continue request smuggling past front-end proxies

Apache Traffic Server parses an unread POST body left on a client connection as a new request when the origin answers early to an Expect: 100-continue request. An attacker behind a front-end proxy that shares connections with Traffic Server can smuggle requests past the front end and desynchronize responses for other users.

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

## How to check

Check the installed Traffic Server version (for example with traffic_server -V) and see whether it falls in 8.0.0-8.1.11, 9.0.0-9.2.15, 10.0.0-10.1.4, or 10.2.0.

## Fix

Upgrade to 9.2.16, 10.1.5, or 10.2.1, per the advisory.

## Timeline

- 2026-10-23T21:57:29+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2025-55702
- 2026-10-24T13:15:54+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2025-55702

## From the sources

When a client sends a POST with Expect: 100-continue and the origin answers before reading the body, Apache Traffic Server parses the unread body left on the client connection as the next request. An attacker behind a front-end proxy that shares connections to Traffic Server can use this to smuggle requests past the front end and desynchronize responses for other users.



This issue affects Apache Traffic Server: from 8.0.0 through 8.1.11, from 9.0.0 through 9.2.15, from 10.0.0 through 10.1.4, 10.2.0.



Users are recommended to upgrade to version 9.2.16, 10.1.5, or 10.2.1, which fix the issue.

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