CVE-2026-23849: File Browser vulnerable to Username Enumeration via Timing Attack in /api/login

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2026-01-19 · updated 2026-06-17
Weakness: CWE-208

Description

File Browser provides a file managing interface within a specified directory and can be used to upload, delete, preview, rename, and edit files. Prior to version 2.55.0, the JSONAuth. Auth function contains a logic flaw that allows unauthenticated attackers to enumerate valid usernames by measuring the response time of the /api/login endpoint. The vulnerability exists due to a "short-circuit" evaluation in the authentication logic. When a username is not found in the database, the function returns immediately. However, if the username does exist, the code proceeds to verify the password using bcrypt (users.CheckPwd), which is a computationally expensive operation designed to be slow. This difference in execution path creates a measurable timing discrepancy. Version 2.55.0 contains a patch for the issue.

Affected products

filebrowser: before 2.55.0 — fixed in 2.55.0

How to fix

Upgrade to a fixed version: filebrowser 2.55.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-23849 or the next vulnerability affects your stack