---
title: "CVE-2026-48777: FileBrowser Quantum: Path traversal in public share PATCH allows file ops outside shared directory"
url: https://erroneo.us/security/cve/CVE-2026-48777/
description: "CVE-2026-48777 (github.com/gtsteffaniak/filebrowser/backend (Go)): FileBrowser Quantum is a free, self-hosted, web-based file manager. Versions prior to…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-16
date_modified: 2026-06-17
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-48777"
kev: false
cvss: 9.3
epss: 0.00522
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-48777: FileBrowser Quantum: Path traversal in public share PATCH allows file ops outside shared directory

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 0.5% , percentile 43: FIRST’s model estimates a 0.5% chance of exploitation activity in the next 30 days, higher than 43% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/gtsteffaniak/filebrowser/backend (Go) < 0.0.0-20260518193514-28e9b81e438e, fixed in 0.0.0-20260518193514-28e9b81e438e . Check your lockfile, including transitive dependencies.

## What it is

FileBrowser Quantum is a free, self-hosted, web-based file manager. Versions prior to 1.3.2-stable, 1.4.0-beta and 1.4.1-beta are vulnerable to Path Traversal through the publicPatchHandler in backend/http/public.go which joins user-controlled fromPath and toPath body fields with the trusted d.share.Path BEFORE the downstream sanitizer runs. Because filepath.Join collapses .. segments during the join, the sanitizer in resourcePatchHandler never sees the traversal and the move/copy/rename operates on a path outside the shared directory. The same root-cause pattern was patched for the bulk DELETE endpoint as CVE-2026-44542 (GHSA-fwj3-42wh-8673), but the PATCH handler with the identical pattern was not updated. A public share link with AllowModify=true is sufficient to exploit this. Anyone holding such a link can move, copy, or rename arbitrary files within the share owner's source root. This issue has been fixed in versions 1.3.3-stable and 1.4.2-beta.

## Affected packages

- Go `github.com/gtsteffaniak/filebrowser/backend` < 0.0.0-20260518193514-28e9b81e438e → fixed: 0.0.0-20260518193514-28e9b81e438e

## Affected products (CVE record)

- gtsteffaniak filebrowser: < 1.3.3-stable, >= 1.4.0-beta, < 1.4.2-beta

## Severity

- GitHub_M CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.52% probability of exploitation activity in the next 30 days; percentile 43.

## Sources

- [GitHub Advisory GHSA-qqqm-5547-774x](https://github.com/advisories/GHSA-qqqm-5547-774x)
- [CVE.org record CVE-2026-48777](https://www.cve.org/CVERecord?id=CVE-2026-48777)
- [NVD entry CVE-2026-48777](https://nvd.nist.gov/vuln/detail/CVE-2026-48777)
- [github.com](https://github.com/gtsteffaniak/filebrowser/security/advisories/GHSA-qqqm-5547-774x)
- [github.com](https://github.com/gtsteffaniak/filebrowser/releases/tag/v1.3.3-stable)
- [github.com](https://github.com/gtsteffaniak/filebrowser/releases/tag/v1.4.2-beta)

---
Source page: https://erroneo.us/security/cve/CVE-2026-48777/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt