Langfuse up to 3.166.x Plaintext Provider LLM API access control

Summaryinfo

A vulnerability classified as critical has been found in Langfuse up to 3.166.x. The affected element is an unknown function of the component Plaintext Provider LLM API. The manipulation leads to access control. This vulnerability is documented as CVE-2026-41487. The attack can be initiated remotely. There is not any exploit available. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Langfuse up to 3.166.x and classified as critical. This issue affects some unknown processing of the component Plaintext Provider LLM API. The manipulation with an unknown input leads to a access control vulnerability. Using CWE to declare the problem leads to CWE-284. The product does not restrict or incorrectly restricts access to a resource from an unauthorized actor. Impacted is confidentiality, integrity, and availability. The summary by CVE is:

Langfuse is an open source large language model engineering platform. From version 3.68.0 to before version 3.167.0, there is a role-based-access control flaw in the LLM connection update flow. An authenticated, low-privileged user of role “member” in a project could request the update of an existing LLM connection to an attacker-controlled baseUrl, causing Langfuse to reuse the stored provider secret and redirect the test request to an attacker-controlled endpoint. This could expose the plaintext provider LLM API key for that connection. The attack is only possible if a user is already part of a project and has “member” scoped access. This issue has been patched in version 3.167.0.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-41487 since 04/20/2026. The exploitation is known to be easy. The attack may be initiated remotely. The technical details are unknown and an exploit is not publicly available. The attack technique deployed by this issue is T1068 according to MITRE ATT&CK.

Upgrading to version 3.167.0 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 7527bb0d84bc0a3dc24a4b16d22ed2e46e6dddff 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.

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Productinfo

Name

• Langfuse

Version

• 3.166

License

• open-source

Website

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

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