CVE-2026-24055: Langfuse Slack OAuth Installation Endpoint Lacks Authentication, Enabling Arbitrary Project Linking

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-22 · updated 2026-06-17
Weakness: CWE-284

Description

Langfuse is an open source large language model engineering platform. In versions 3.146.0 and below, the /api/public/slack/install endpoint initiates Slack OAuth using a projectId provided by the client without authentication or authorization. The projectId is preserved throughout the OAuth flow, and the callback stores installations based on this untrusted metadata. This allows an attacker to bind their Slack workspace to any project and potentially receive changes to prompts stored in Langfuse Prompt Management. An attacker can replace existing Prompt Slack Automation integrations or pre-register a malicious one, though the latter requires an authenticated user to unknowingly configure it despite visible workspace and channel indicators in the UI. This issue has been fixed in version 3.147.0.

Affected products

langfuse: from 3.89.0 before 3.147.0 — fixed in 3.147.0

How to fix

Upgrade to a fixed version: langfuse 3.147.0. Check the vendor advisory for mitigations.

References

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