File Browser Vulnerable to Username Enumeration via Timing Attack in /api/login

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

5.3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS

• CVE-2026-23849: 0.48% estimated exploitation activity in the next 30 days; percentile 41.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Details 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: Invalid User: ~1ms execution (Database lookup only). Valid User: ~50ms+ execution (Database lookup + Bcrypt hashing). In auth/json.go: PoC The following Python script automates the attack. It first calibrates the network latency using random (non-existent) users to establish a baseline/threshold, and then tests a list of target usernames. Valid users are detected when the response…

Published by the source

21 Jan 2026, 01:02 UTC

Last modified by the source

3 Feb 2026, 17:22 UTC

Source last checked

26 Oct 2026, 15:14 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-43mm-m3h2-3prc

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# Patch Next advisory brief: CVE-2026-23849

Advisory: File Browser Vulnerable to Username Enumeration via Timing Attack in /api/login
IDs: CVE-2026-23849, GHSA-43mm-m3h2-3prc
Record: https://patchnext.com/advisories/cve-2026-23849 (revision 1, source checked 26 Oct 2026, 15:14 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/filebrowser/filebrowser/v2 2.55.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/filebrowser/filebrowser/v2: affected < 2.55.0; fixed in 2.55.0
- Go github.com/filebrowser/filebrowser: affected <= 1.11.0

## Suggested inspection (read-only)
- Go github.com/filebrowser/filebrowser/v2: check the installed version with your package manager.
- Go github.com/filebrowser/filebrowser: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/filebrowser/filebrowser/v2, github.com/filebrowser/filebrowser.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-43mm-m3h2-3prc (GitHub-reviewed advisory GHSA-43mm-m3h2-3prc lists affected ranges: Go github.com/filebrowser/filebrowser >=0 =0 <2.55.0)

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