HTTP Request Smuggling in Http4s <1.0.0-M45 & <0.23.31 Trailer Handling
CVE-2025-59822 Published on September 23, 2025
Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section
Http4s is a Scala interface for HTTP services. In versions from 1.0.0-M1 to before 1.0.0-M45 and before 0.23.31, 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, and poison web caches. A pre-requisite for exploitation involves the web application being deployed behind a reverse-proxy that forwards trailer headers. This issue has been patched in versions 1.0.0-M45 and 0.23.31.
Vulnerability Analysis
CVE-2025-59822 is exploitable with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. Public availability of a proof of concept (POC) exploit exists for CVE-2025-59822. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
What is a HTTP Request Smuggling Vulnerability?
When malformed or abnormal HTTP requests are interpreted by one or more entities in the data flow between the user and the web server, such as a proxy or firewall, they can be interpreted inconsistently, allowing the attacker to "smuggle" a request to one device without the other device being aware of it.
CVE-2025-59822 has been classified to as a HTTP Request Smuggling vulnerability or weakness.
Affected Versions
http4s:- Version < 0.23.31 is affected.
- Version >= 1.0.0-M1, < 1.0.0-M45 is affected.
Vulnerable Packages
The following package name and versions may be associated with CVE-2025-59822
| Package Manager | Vulnerable Package | Versions | Fixed In |
|---|---|---|---|
| maven | org.http4s:http4s-ember-core_2.12 | < 0.23.31 | 0.23.31 |
| maven | org.http4s:http4s-ember-core_2.13 | < 0.23.31 | 0.23.31 |
| maven | org.http4s:http4s-ember-core_3 | < 0.23.31 | 0.23.31 |
| maven | org.http4s:http4s-ember-core_2.13 | >= 1.0.0-M1, < 1.0.0-M45 | 1.0.0-M45 |
| maven | org.http4s:http4s-ember-core_3 | >= 1.0.0-M1, < 1.0.0-M45 | 1.0.0-M45 |
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.