Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section

Exploitation

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

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2025-59822: 0.37% estimated exploitation activity in the next 30 days; percentile 31.40 (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 http4s is vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section. This vulnerability could enable attackers to: - Bypass front-end servers security controls - Launch targeted attacks against active users - Poison web caches Pre-requisites for the exploitation: the web appication has to be deployed behind a reverse-proxy that forwards trailer headers. Details The HTTP chunked message parser, after parsing the last body chunk, calls parseTrailers (ember-core/shared/src/main/scala/org/http4s/ember/core/ChunkedEncoding.scala#L122-142). This method parses the trailer section using Parser.parse, where the issue originates. parse has a bug that allows to terminate the parsing before finding the double CRLF condition: when it finds an header line that does not include the colon character, it continues parsing with state=false looking for the header name till reaching the condition else if (current == lf && (idx 0 && message(idx - 1) == cr)) that sets…

Published by the source

23 Sep 2025, 17:37 UTC

Last modified by the source

13 Oct 2025, 15:20 UTC

Source last checked

26 Oct 2026, 16:40 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-wcwh-7gfw-5wrr

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# Patch Next advisory brief: CVE-2025-59822

Advisory: Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section
IDs: CVE-2025-59822, GHSA-wcwh-7gfw-5wrr
Record: https://patchnext.com/advisories/cve-2025-59822 (revision 1, source checked 26 Oct 2026, 16:40 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.http4s:http4s-ember-core_2.12 0.23.31; org.http4s:http4s-ember-core_3 1.0.0-M45, 0.23.31; org.http4s:http4s-ember-core_2.13 1.0.0-M45, 0.23.31. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.http4s:http4s-ember-core_2.12: affected < 0.23.31; fixed in 0.23.31
- Maven org.http4s:http4s-ember-core_3: affected < 0.23.31; >= 1.0.0-M1, < 1.0.0-M45; fixed in 0.23.31, 1.0.0-M45
- Maven org.http4s:http4s-ember-core_2.13: affected < 0.23.31; >= 1.0.0-M1, < 1.0.0-M45; fixed in 0.23.31, 1.0.0-M45

## Suggested inspection (read-only)
- Maven org.http4s:http4s-ember-core_2.12: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_3: check the installed version with your package manager.
- Maven org.http4s:http4s-ember-core_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:http4s-ember-core_2.12, org.http4s:http4s-ember-core_3, org.http4s:http4s-ember-core_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-wcwh-7gfw-5wrr (GitHub-reviewed advisory GHSA-wcwh-7gfw-5wrr lists affected ranges: Maven org.http4s:http4s-ember-core_2.12 >=0 =0 =1.0.0-M1 =0 =1.0.0-M1 <1.0.0-M45)

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