---
id: CVE-2026-73494
title: >-
  blaze is a Scala library for building asynchronous pipelines, with a focus on
  network IO
summary: >-
  blaze is a Scala library for building asynchronous pipelines, with a focus on
  network IO. Prior to 0.23.18 and from 1.0.0-M1 until 1.0.0-M42, five HTTP/1.1
  conformance laxities in the hand-written Java parser under
  http/src/main/java/org…
severity: high
cvss: 7.4
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N'
cwe:
  - CWE-444
vendor: http4s
product: blaze
affected:
  - blaze < 0.23.18
  - 'blaze >= 1.0.0-M1, < 1.0.0-M42'
  - blaze-http_2.13 < 0.23.18
  - 'blaze-http_2.13 >= 1.0.0-M1, < 1.0.0-M42'
  - blaze-http_3 < 0.23.18
  - 'blaze-http_3 >= 1.0.0-M1, < 1.0.0-M42'
  - http4s-blaze-server_2.13 < 0.23.18
published: '2026-09-14'
updated: '2026-09-14'
sourceUpdated: '2026-09-14T20:16:50.707'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-73494'
references:
  - url: >-
      https://github.com/http4s/blaze/commit/3f7c022e306631b006dcb43a1d7f65c0d1966f17
    label: security-advisories@github.com
  - url: >-
      https://github.com/http4s/blaze/commit/4eec2007806aa9acfefb00ebb636ddc39a147a96
    label: security-advisories@github.com
  - url: >-
      https://github.com/http4s/blaze/commit/927b67753a78c13c4445dac9307f511f5c4878c3
    label: security-advisories@github.com
  - url: >-
      https://github.com/http4s/blaze/commit/a54bc9cd31758335c7f24e29763622fd03fcf734
    label: security-advisories@github.com
  - url: >-
      https://github.com/http4s/blaze/commit/c47d9675f87603f11b32a11d503626bdf9be5c7a
    label: security-advisories@github.com
  - url: >-
      https://github.com/http4s/blaze/commit/e871ebb1d27f50c98fd56988526ce42d0fee74d6
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/blaze/releases/tag/v0.23.18'
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/blaze/releases/tag/v1.0.0-M42'
    label: security-advisories@github.com
  - url: 'https://github.com/http4s/blaze/security/advisories/GHSA-mhvj-jhpq-885v'
    label: security-advisories@github.com
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'no'
  technicalImpact: total
  timestamp: '2026-09-14T19:21:20.842876Z'
ingestedAt: '2026-09-14T19:13:23.460Z'
epss: 0.00628
epssPercentile: 0.47863
---

## Overview

blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and from 1.0.0-M1 until 1.0.0-M42, five HTTP/1.1 conformance laxities in the hand-written Java parser under http/src/main/java/org/http4s/blaze/http/parser/ can cause blaze to derive a different request boundary than a stricter fronting intermediary. A default BlazeServerBuilder accepts invalid or valueless header field names that violate tchar syntax, obsolete folded field lines (obs-fold), unsupported Transfer-Encoding values, duplicate Content-Length fields, and requests containing both Transfer-Encoding and Content-Length. If a lenient or legacy proxy forwards the malformed bytes but interprets them differently, the disagreement can permit front-end authorization bypass, response-queue poisoning on pooled backend connections, or cache poisoning. Exploitation requires a pair of disagreeing parsers; no non-default blaze configuration is required. The affected checks are enforced in BodyAndHeaderParser and Http1ServerParser. This issue is fixed in versions 0.23.18 and 1.0.0-M42.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.