Http4s up to 0.23.34/1.0.0-M46 Ember HeaderP.parse request smuggling

Summaryinfo

A vulnerability classified as problematic has been found in Http4s up to 0.23.34/1.0.0-M46. This affects the function HeaderP.parse of the component Ember. This manipulation causes request smuggling. The identification of this vulnerability is CVE-2026-69205. It is possible to initiate the attack remotely. There is no exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in Http4s up to 0.23.34/1.0.0-M46 and classified as problematic. Affected by this vulnerability is the function HeaderP.parse of the component Ember. The manipulation with an unknown input leads to a request smuggling vulnerability. The CWE definition for the vulnerability is CWE-444. The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination. As an impact it is known to affect integrity. The summary by CVE is:

Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, Ember’s HeaderP.parse uses a case-sensitive substring test for the Transfer-Encoding value and decodes header bytes with the platform default charset. Values such as Chunked are not recognized, values such as notchunked are incorrectly accepted, and Unicode case folding can turn a Kelvin-sign byte sequence into a match when UTF-8 is used. Intermediaries that apply RFC-compliant token and charset rules can therefore disagree with Ember’s Content-Length or zero-length framing, enabling TE.CL or TE.0 request smuggling, access-control bypass, cross-user request hijacking, and cache poisoning on the server path. Response smuggling through an ember-client gateway requires a malicious or compromised upstream. This issue is fixed in versions 0.23.35 and 1.0.0-M47.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-69205 since 08/03/2026. The exploitation appears to be easy. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 0.23.35 or 1.0.0-M47 eliminates this vulnerability.

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Productinfo

Name

• Http4s

Version

• 0.23.0
• 0.23.1
• 0.23.2
• 0.23.3
• 0.23.4
• 0.23.5
• 0.23.6
• 0.23.7
• 0.23.8
• 0.23.9
• 0.23.10
• 0.23.11
• 0.23.12
• 0.23.13
• 0.23.14
• 0.23.15
• 0.23.16
• 0.23.17
• 0.23.18
• 0.23.19
• 0.23.20
• 0.23.21
• 0.23.22
• 0.23.23
• 0.23.24
• 0.23.25
• 0.23.26
• 0.23.27
• 0.23.28
• 0.23.29
• 0.23.30
• 0.23.31
• 0.23.32
• 0.23.33
• 0.23.34
• 1.0.0-M46

Website

• Product: https://github.com/http4s/http4s/

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