Zulip up to 12.1 Markdown Rendering /messages/render content allocation of resources

Summaryinfo

A vulnerability labeled as problematic has been found in Zulip up to 12.1. Affected by this issue is some unknown functionality of the file /messages/render of the component Markdown Rendering. Such manipulation of the argument content leads to allocation of resources. This vulnerability is listed as CVE-2026-97701. The attack may be performed from remote. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability was found in Zulip up to 12.1 and classified as problematic. Affected by this issue is an unknown part of the file /messages/render of the component Markdown Rendering. The manipulation of the argument content with an unknown input leads to a allocation of resources vulnerability. Using CWE to declare the problem leads to CWE-770. The product allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor. Impacted is availability. CVE summarizes:

Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-97701 since 09/24/2026. The exploitation is known to be easy. The attack may be launched remotely. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1499.

Upgrading to version 12.2 eliminates this vulnerability.

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Productinfo

Name

• Zulip

Version

• 12.0
• 12.1

Website

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

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