CVE-2017-10784

What it actually does

The flaw permits remote injection of terminal escape sequences into WEBrick access logs through the username field of Basic authentication headers, which can be interpreted by vulnerable terminal emulators to execute arbitrary commands when logs are viewed.

Why it matters to the business

Attackers may gain unauthorized command execution on systems where administrators or monitoring tools view server logs, potentially leading to full system compromise, data theft, or service disruption across Ruby-based web applications.

How an attack unfolds

An attacker crafts a Basic authentication header containing a username with embedded ANSI escape sequences, sends it to a vulnerable WEBrick server, and the sequences are written to the access log. When an administrator or automated process displays the log in a terminal emulator that processes escape codes, the sequences trigger arbitrary command execution.

How to fix it

Upgrade Ruby to version 2.2.8 or later, 2.3.5 or later, or 2.4.2 or later. If immediate upgrade is not possible, disable Basic authentication or implement input sanitization on usernames before logging.

How to confirm the fix worked

Verify the installed Ruby version is at or above the fixed releases listed in remediation. Review WEBrick source or changelog for the authentication logging fix. Test by sending a crafted auth request and confirming escape sequences are no longer logged verbatim.

Typical attack path

1. Identify a target running an affected WEBrick version via banner or behavior
2. Craft a Basic auth username containing terminal escape sequences for command injection
3. Issue an HTTP request with the malicious Authorization header
4. Confirm the crafted entry appears in server access logs
5. Wait for or trigger log viewing in a vulnerable terminal to execute injected commands

How to detect it

Search web server access logs for Basic auth entries containing control characters or ANSI escape sequences in the username field. Correlate with timestamps of log viewing processes or administrator terminal sessions. Examine any post-exploitation artifacts such as unexpected processes spawned from terminal sessions.

• Authorization: Basic.*[\x1b\x9b]
• usernames containing \x1b[
• WEBrick access log entries with non-printable characters in auth user field

What your security team should do

• Prioritize upgrade of all Ruby installations to patched versions given the public disclosure and stable exploitability score
• Audit web server configurations to ensure Basic auth is not exposed on internet-facing endpoints
• Implement log sanitization or use log viewers that disable escape sequence processing
• Monitor for unusual authentication attempts and review historical logs for control characters in usernames