---
id: "CVE-2026-55614"
kind: "vulnerability"
aliases: ["CVE-2026-55614"]
title: "uhttpd: mixed-case Transfer-Encoding header enables HTTP request smuggling"
severity: "medium"
cvss: 6.9
epss: null
exploited: false
status: "open"
category: "runtime"
products: []
ecosystems: []
tags: ["embedded", "http-server", "openwrt", "runtime", "uhttpd"]
not_affected_if: ["default-config", "uhttpd-not-deployed"]
published_at: "2026-10-30T22:16:55+00:00"
first_seen_at: "2026-10-30T22:25:56+00:00"
updated_at: "2026-10-30T22:27:12+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55614", "first_seen_at": "2026-10-30T22:25:56+00:00"}]
---

# uhttpd: mixed-case Transfer-Encoding header enables HTTP request smuggling

uhttpd, a small HTTP server, compares the Transfer-Encoding header value to "chunked" case-sensitively, so a mixed-case value is accepted without chunked parsing being enabled. On keep-alive connections the unread chunked POST body is parsed as a second request, enabling request smuggling and desynchronization.

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

## How to check

- Check whether the running uhttpd build includes commit `ae015e099986ceace44975cb69629841a2d58d37` or `6641b050e5f7c7fd9ae92e8e119d6d6dfc6e9837`
- Look for `client_parse_header()` in `client.c` and confirm the Transfer-Encoding comparison is case-insensitive
- Identify whether uhttpd sits behind a proxy or handles keep-alive POST traffic directly

## Fix

- Apply the patches in commits `ae015e099986ceace44975cb69629841a2d58d37` and `6641b050e5f7c7fd9ae92e8e119d6d6dfc6e9837`
- Fixed release version: unknown

## Timeline

- 2026-10-30T22:25:56+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-55614

## From the sources

uhttpd is a small HTTP server. In unpatched repository snapshots, `client_parse_header()` in `client.c` lowercases header names but compares the `Transfer-Encoding` value to `chunked` using case-sensitive `strcmp`. A mixed-case transfer-coding token is accepted without enabling `r->transfer_chunked`, despite transfer-coding tokens being case-insensitive. On a keep-alive connection, the `chunked` POST body is left unread and request-shaped body bytes are parsed as another HTTP request, permitting HTTP request smuggling and boundary desynchronization. Commits ae015e099986ceace44975cb69629841a2d58d37 and 6641b050e5f7c7fd9ae92e8e119d6d6dfc6e9837 patch the issue.

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