miguelgrinberg microdot up to 2.6.0 Response.set_cookie response splitting

Summaryinfo

A vulnerability was found in miguelgrinberg microdot up to 2.6.0. It has been rated as problematic. This vulnerability affects the function Response.set_cookie. This manipulation causes response splitting. This vulnerability is handled as CVE-2026-42874. The attack can be initiated remotely. There is not any exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability was found in miguelgrinberg microdot up to 2.6.0. It has been declared as problematic. Affected by this vulnerability is the function Response.set_cookie. The manipulation with an unknown input leads to a response splitting vulnerability. The CWE definition for the vulnerability is CWE-113. The product receives data from an HTTP agent/component (e.g., web server, proxy, browser, etc.), but it does not neutralize or incorrectly neutralizes CR and LF characters before the data is included in outgoing HTTP headers. As an impact it is known to affect integrity. The summary by CVE is:

Microdot is a minimalistic Python web framework. Prior to 2.6.1, the Response.set_cookie() method does not sanitize its string arguments, and in particular will not detect the presence of the \r\n sequence in them. This can be a potential source of header injection attacks. For a header injection attack through this issue to be possible, an attacker must first infiltrate the client (for example through an independent XSS attack), so that it can send malicious information that is destined to be stored in a cookie by the server on behalf of the victim. An attacker that infiltrates one client can only orchestrate a header injection attack for that client, all other clients that were not infiltrated are safe. This vulnerability is fixed in 2.6.1.

The advisory is shared at github.com. This vulnerability is known as CVE-2026-42874 since 04/30/2026. The exploitation appears to be difficult. The attack can be launched remotely. The exploitation doesn't need any form of authentication. Technical details are known, but no exploit is available.

Upgrading to version 2.6.1 eliminates this vulnerability. Applying the patch 99b281b45faef8472410f2d56bfef496dfbd95d5 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Vendor

• miguelgrinberg

Name

• microdot

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6.0

License

• open-source

Website

• Product: https://github.com/miguelgrinberg/microdot/

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Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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