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CVE-2026-54088 – Pre-Auth RCE via OS Command Injection – File Browser < 2.63.6

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Summary

CVE-2026-54088 is a critical pre-authentication OS command injection vulnerability in File Browser (filebrowser/filebrowser), a widely deployed open-source web-based file management interface. The flaw exists in the Hook Authentication feature, where user-supplied credentials are interpolated into shell command strings using os.Expand without any sanitization, allowing an unauthenticated remote attacker to execute arbitrary OS commands on the server before authentication takes place. This vulnerability carries a CVSS 4.0 score of 9.3 (Critical) and is fixed in version 2.63.6.

Technical details

  • Root cause: In auth/hook.go, the HookAuth.RunCommand function uses Go’s os.Expand() to interpolate the user-supplied username and password fields directly into the configured hook command string. No escaping, quoting, or input validation is applied prior to shell execution.
  • Trigger conditions: The Hook Authentication feature must be enabled by an administrator (non-default configuration). When enabled, any login attempt — including from unauthenticated users — passes credentials through the hook command, making the attack surface reachable with no prior access.
  • Attack vector: An unauthenticated remote attacker submits a crafted username or password containing shell metacharacters at the File Browser login screen. For example, if the configured command is sh -c "test $USERNAME = 'admin'", injecting ; id # as the username expands to sh -c "test ; id # = 'admin'", causing the injected command to execute with File Browser’s process privileges.
  • Impact: Full pre-authentication remote code execution (RCE). Successful exploitation yields complete compromise of confidentiality, integrity, and availability of the host system (CVSS VC:H/VI:H/VA:H). Attackers gain OS-level command execution as the user running the File Browser process.
  • Weaknesses: CWE-78 (OS Command Injection), CWE-88 (Argument Injection), CWE-306 (Missing Authentication for Critical Function).
  • Public PoC available: A proof-of-concept exploit repository was publicly indexed on June 12, 2026 (https://github.com/Saku0512/CVE-2026-54088-poc).

Affected software

  • File Browser all versions prior to 2.63.6 when the Hook Authentication feature is enabled.

Severity

  • CVSS 4.0 Base Score: 9.3 (Critical)
  • CVSS 4.0 Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate — Patch: Upgrade File Browser to version 2.63.6 or later, which addresses this vulnerability.
  • If immediate patching is not possible — Workaround: Disable the Hook Authentication feature. Removing the hook command configuration eliminates the vulnerable code path entirely, reducing exposure until an upgrade can be performed.
  • Network mitigation: Restrict internet-facing access to File Browser instances. Ensure that any deployment not requiring external access is placed behind a firewall or network access controls to limit the reachable attack surface.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

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