---
id: GHSA-46q4-43ph-c6fr
title: >-
  blaze: Chunked-body trailer fields promoted into Request.headers in
  blaze-server (front-end header-sanitization bypass)
summary: >-
  blaze: Chunked-body trailer fields promoted into Request.headers in
  blaze-server (front-end header-sanitization bypass)
severity: high
cvss: 7.4
cwe:
  - CWE-444
vendor: http4s
product: 'org.http4s:blaze-http_2.13'
ecosystem: maven
affected:
  - 'org.http4s:blaze-http_2.13 <= 0.23.17'
  - 'org.http4s:blaze-http_2.12 <= 0.23.17'
  - 'org.http4s:blaze-http_3 <= 0.23.17'
  - 'org.http4s:blaze-http_3 >= 1.0.0-M1, < 1.0.0-M42'
  - 'org.http4s:blaze-http_2.13 >= 1.0.0-M1, <= 1.0.0-M41'
patched:
  - 'org.http4s:blaze-http_2.13 0.23.18'
  - 'org.http4s:blaze-http_2.12 0.23.18'
  - 'org.http4s:blaze-http_3 0.23.18'
  - 'org.http4s:blaze-http_3 1.0.0-M42'
  - 'org.http4s:blaze-http_2.13 1.0.0-M42'
published: '2026-07-24'
updated: '2026-07-24'
source: GHSA
sourceUrl: 'https://github.com/advisories/GHSA-46q4-43ph-c6fr'
references:
  - url: 'https://github.com/http4s/blaze/security/advisories/GHSA-46q4-43ph-c6fr'
  - url: >-
      https://github.com/http4s/blaze/commit/ef3e666c146cfc16cb6603f1fc3c464daab4a24f
  - url: 'https://github.com/http4s/blaze/releases/tag/v0.23.18'
  - url: 'https://github.com/http4s/blaze/releases/tag/v1.0.0-M42'
  - url: 'https://github.com/advisories/GHSA-46q4-43ph-c6fr'
tags:
  - ghsa
  - maven
ingestedAt: '2026-07-24T22:40:26.707Z'
---

## Overview

### Summary
  blaze-server can merge HTTP/1.1 chunked-body trailer fields into `Request.headers`. Because trailer fields are attacker-controlled, an unauthenticated remote client can inject arbitrary header names/values (e.g. `X-Forwarded-For`, internal-auth headers) that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application.

  ### Impact
  Any http4s application using `BlazeServerBuilder` over HTTP/1.1 whose routes or middleware trust proxy-set headers (e.g., `X-Forwarded-For`, `X-Real-IP`, `X-Forwarded-Host`, org-internal auth headers) is affected. Where a fronting proxy strips/normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists/rate-limits/audit, forge the `https` scheme, or inject internal-auth headers. A promoted `Connection: close` trailer is also honored, allowing attacker-controlled termination of pooled backend connections.

  ### Workarounds
  Deploy behind a proxy that removes trailer fields (or rejects requests that use trailers) before forwarding; until patched, avoid trust decisions based on headers that a proxy is relied upon to sanitize.

## Affected packages

- `org.http4s:blaze-http_2.13 <= 0.23.17`
- `org.http4s:blaze-http_2.12 <= 0.23.17`
- `org.http4s:blaze-http_3 <= 0.23.17`
- `org.http4s:blaze-http_3 >= 1.0.0-M1, < 1.0.0-M42`
- `org.http4s:blaze-http_2.13 >= 1.0.0-M1, <= 1.0.0-M41`

## Remediation

Upgrade to a patched release:

- `org.http4s:blaze-http_2.13 0.23.18`
- `org.http4s:blaze-http_2.12 0.23.18`
- `org.http4s:blaze-http_3 0.23.18`
- `org.http4s:blaze-http_3 1.0.0-M42`
- `org.http4s:blaze-http_2.13 1.0.0-M42`