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

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.4 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2026-73494: 0.63% estimated exploitation activity in the next 30 days; percentile 50.14 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary Five independent HTTP/1.1 conformance laxities in blaze's hand-written Java parser (http/src/main/java/org/http4s/blaze/http/parser/) cause request-boundary disagreement with a stricter intermediary. All are reachable from a default BlazeServerBuilder with no non-default configuration. Impact Actual exploitability depends on the fronting proxy — a boundary disagreement requires a pair of parsers that disagree. Where the proxy forwards the malformed bytes and derives a different message boundary, the consequences are the standard set: front-end ACL/auth bypass, response-queue poisoning on pooled backend connections, and cache poisoning. Risk concentrates on lenient or legacy intermediaries. Workarounds Deploy behind an RFC-strict reverse proxy (nginx, HAProxy, Envoy, ALB) that rejects or re-serializes malformed requests at the edge; this neutralizes most of these for deployments that cannot upgrade immediately.

Published by the source

24 Jul 2026, 22:26 UTC

Last modified by the source

12 Aug 2026, 21:12 UTC

Source last checked

26 Oct 2026, 16:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-mhvj-jhpq-885v

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# Patch Next advisory brief: CVE-2026-73494

Advisory: blaze: Multiple HTTP/1.1 request-smuggling primitives in blaze's Java wire parser
IDs: CVE-2026-73494, GHSA-mhvj-jhpq-885v
Record: https://patchnext.com/advisories/cve-2026-73494 (revision 1, source checked 26 Oct 2026, 16:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.4)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.http4s:blaze-http_3 1.0.0-M42, 0.23.18; org.http4s:blaze-http_2.13 1.0.0-M42, 0.23.18; org.http4s:http4s-blaze-server_2.13 0.23.18. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4s:blaze-http_3: affected <= 0.23.17; >= 1.0.0-M1, <= 1.0.0-M41; fixed in 1.0.0-M42, 0.23.18
- Maven org.http4s:blaze-http_2.13: affected <= 0.23.17; >= 1.0.0-M1, <= 1.0.0-M41; fixed in 1.0.0-M42, 0.23.18
- Maven org.http4s:http4s-blaze-server_2.13: affected <= 0.23.17; fixed in 0.23.18

## Suggested inspection (read-only)
- Maven org.http4s:blaze-http_3: check the installed version with your package manager.
- Maven org.http4s:blaze-http_2.13: check the installed version with your package manager.
- Maven org.http4s:http4s-blaze-server_2.13: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.http4s:blaze-http_3, org.http4s:blaze-http_2.13, org.http4s:http4s-blaze-server_2.13.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-mhvj-jhpq-885v (GitHub-reviewed advisory GHSA-mhvj-jhpq-885v lists affected ranges: Maven org.http4s:http4s-blaze-server_2.13 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <=1.0.0-M41)

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