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

> Unauthenticated attackers can enumerate valid usernames in File Browser by measuring response time differences during login attempts.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 19 Jan 2026
- **Updated:** 20 Jan 2026
- **Also known as:** GHSA-43mm-m3h2-3prc, GO-2026-4344

## What is CVE-2026-23849?

CVE-2026-23849 is a medium-severity vulnerability in filebrowser, published on 19 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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.

Weakness: CWE-203 (Observable Discrepancy), CWE-208 (Observable Timing Discrepancy)

## Which versions are affected by CVE-2026-23849?

6 open source packages ship an affected version, including github.com/filebrowser/filebrowser and github.com/filebrowser/filebrowser/v2. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/filebrowser/filebrowser` | Go | All versions | None |
| `github.com/filebrowser/filebrowser` | Go | All versions to 1.11.0 | None |
| `github.com/filebrowser/filebrowser` | Go | All versions to 1.11.0 | None |
| `github.com/filebrowser/filebrowser/v2` | Go | All versions | 2.55.0 |
| `github.com/filebrowser/filebrowser/v2` | Go | All versions | 2.55.0 |
| `github.com/filebrowser/filebrowser/v2` | Go | All versions | 2.55.0 |

Products: Filebrowser Filebrowser.

## How do I fix CVE-2026-23849?

Upgrade to a fixed version.

## Is CVE-2026-23849 being exploited?

There is no known exploitation of CVE-2026-23849 in the wild and no public exploit code.

## Other vulnerabilities in filebrowser

- [CVE-2026-32760](https://insights.sbomify.com/CVE-2026-32760/): File Browser Self Registration Grants Any User Admin Access When Default Permissions Include Admin (critical 10.0)
- [CVE-2026-29188](https://insights.sbomify.com/CVE-2026-29188/): File Browser: TUS Delete Endpoint Bypasses Delete Permission Check (critical 9.1)
- [CVE-2023-39612](https://insights.sbomify.com/CVE-2023-39612/): Cross-site scripting in n/a (critical 9.0)
- [CVE-2026-30934](https://insights.sbomify.com/CVE-2026-30934/): FileBrowser Quantum: Stored XSS in public share page via unsanitized share metadata (text/template misuse) (high 8.9)
- [CVE-2021-46398](https://insights.sbomify.com/CVE-2021-46398/): Cross-Site Request Forgery in Filebrowser (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23849 and fix it if it is affected.

What it is: CVE-2026-23849 is a medium-severity vulnerability in filebrowser, published on 19 Jan 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-23849 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/filebrowser/filebrowser (Go): affected all versions; no fix listed
- github.com/filebrowser/filebrowser (Go): affected all versions up to 1.11.0; no fix listed
- github.com/filebrowser/filebrowser (Go): affected all versions up to 1.11.0; no fix listed
- github.com/filebrowser/filebrowser/v2 (Go): affected all versions; fixed in 2.55.0
- github.com/filebrowser/filebrowser/v2 (Go): affected all versions; fixed in 2.55.0
- github.com/filebrowser/filebrowser/v2 (Go): affected all versions; fixed in 2.55.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-23849/ (Markdown: https://insights.sbomify.com/CVE-2026-23849/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23849
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23849
- OSV: https://osv.dev/vulnerability/CVE-2026-23849

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-23849/
Summaries are generated and may contain mistakes; the official description above is the record.