CVE-2026-54089: File Browser: Authentication Bypass via Proxy Auth Header Forgery

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 49: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 49% 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/filebrowser/filebrowser/v2 (Go) >= 2.0.0-rc.1, <= 2.63.18, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

File Browser is a file managing interface for uploading, deleting, previewing, renaming, and editing files within a specified directory. Starting with 2.0.0-rc.1, when FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization. This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.

From the GitHub advisory

Summary

When FileBrowser is configured with proxy authentication (auth.method=proxy), any unauthenticated attacker who can reach the server directly can impersonate any user - including admin - by sending a single forged HTTP header. No credentials are required. Additionally, specifying a non-existent username causes the server to automatically create a new user account, providing an account creation primitive with no authorization.

This is an already known issue that has been documented in the documentation for several years, but has not been documented as a vulnerability before.

Severity

HIGH - CVSS 3.1: 8.1 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N)

Weakness type: CWE-287, CWE-290.

Product: github.com/filebrowser/filebrowser/v2 (Go) · Assigned by: GitHub_M · Published: 2026-06-25

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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): 0.61% probability of exploitation activity in the next 30 days; percentile 49.

Timeline

• 2026-06-25 — CVE record last updated
• 2026-06-25 — CVE record published by GitHub_M
• 2026-07-10 — GitHub-reviewed advisory GHSA-xqp3-jq6g-x3qm published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-xqp3-jq6g-x3qm github.com
2. CVE.org record CVE-2026-54089 cve.org
3. NVD entry CVE-2026-54089 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

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