Auth bypass in Langfuse

CVE-2026-24055

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.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N.

EPSS exploit prediction

EPSS: 0.004 (35.9th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.9% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-24055: held from 0.004 to 0.004.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000

Affected products

  • Langfuse — versions >= 3.89.0, < 3.147.0

Weakness classification (CWE)

Public proof-of-concept exploits

References

Frequently asked questions

What is CVE-2026-24055?
CVE-2026-24055 is a medium-severity vulnerability in Langfuse, classified under Improper Access Control. CVSS score: 5.3/10. Published 2026-01-22.
How severe is CVE-2026-24055?
Medium severity. CVSS v3 base score is 5.3 out of 10.
Is CVE-2026-24055 known to be exploited?
1 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.