CVE-2026-54088: File Browser: Command Injection via Authentication Hook Shell Substitution (Pre-Authentication RCE)

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 0.8%, percentile 55: FIRST’s model estimates a 0.8% chance of exploitation activity in the next 30 days, higher than 55% of all scored CVEs (moderate). 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) <= 2.63.5, fixed in 2.63.6. 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. Prior to 2.63.6, the Hook Authentication feature in File Browser allows administrators to delegate login verification to an external shell command. User-supplied credentials (username and password) are interpolated into this command string using os.Expand without sanitization. An unauthenticated remote attacker can inject shell metacharacters in the username or password field at the login screen, causing the server to execute arbitrary OS commands before any authentication takes place. This is a critical pre-authentication RCE. This vulnerability is fixed in 2.63.6.

From the GitHub advisory

Overview

The Hook Authentication feature in File Browser allows administrators to delegate login verification to an external shell command. User-supplied credentials (username and password) are interpolated into this command string using os.Expand without sanitization. An unauthenticated remote attacker can inject shell metacharacters in the username or password field at the login screen, causing the server to execute arbitrary OS commands before any authentication takes place. This is a critical pre-authentication RCE.

Affected Location

- File: auth/hook.go - Function: HookAuth.RunCommand

CVSS v4.0

Weakness type: CWE-78, CWE-88, CWE-306.

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
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

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 partial.
• FIRST EPSS (model of 2026-10-21): 0.76% probability of exploitation activity in the next 30 days; percentile 55.

Timeline

• 2026-06-25 — CVE record last updated
• 2026-06-25 — CVE record published by GitHub_M
• 2026-07-10 — GitHub-reviewed advisory GHSA-m93h-4hw7-5qcm 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-m93h-4hw7-5qcm github.com
2. CVE.org record CVE-2026-54088 cve.org
3. NVD entry CVE-2026-54088 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com

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