CVE-2009-5147

What it actually does

DL::dlopen accepts and resolves library paths derived from tainted strings, bypassing Ruby's taint checks and enabling load of attacker-controlled shared objects that execute arbitrary code during symbol resolution.

Why it matters to the business

Applications built on the listed Ruby releases can be tricked into executing attacker-supplied native code, leading to full host compromise, data theft, or service disruption; the issue affects a wide range of legacy Ruby deployments still present in many environments.

How an attack unfolds

An attacker supplies a tainted string containing a malicious library path or name to any code path that reaches DL::dlopen; Ruby resolves and loads the library without sanitization, the library's initialization routines run with the privileges of the Ruby process, and the attacker gains code execution.

How to fix it

Upgrade Ruby to a release that enforces taint checks inside DL::dlopen (1.8 branch after the relevant patch, 1.9.3 patchlevel 648 or later, 2.0.0 patchlevel 648 or later, 2.1.8 or later); where upgrade is impossible, remove or wrap all direct calls to DL::dlopen and avoid passing untrusted strings to any FFI or dynamic-loading API.

How to confirm the fix worked

After patching, confirm that attempts to pass tainted strings to dlopen raise SecurityError; scan source and gem code for direct or indirect use of DL.dlopen, Fiddle::Function, or similar APIs and ensure all path arguments are untainted or explicitly validated.

Typical attack path

1. Identify an application endpoint or input that reaches DL::dlopen with user-controlled data
2. Craft a tainted library name or path that points to attacker-controlled object code
3. Trigger the dlopen call so Ruby loads the malicious library
4. Execute native code from the library's constructors or exported functions

How to detect it

Review web-application or script logs for unexpected library names or paths containing user input; look for child processes spawned by Ruby that load shared objects from temporary or user-controlled directories; examine core dumps or strace output for dlopen calls with tainted arguments.

What your security team should do

• Inventory all Ruby 1.8–2.1 installations and schedule immediate upgrades to supported releases
• Add static-analysis rules that flag any use of DL::dlopen or equivalent dynamic loaders
• Block execution of unexpected .so/.dll files from application-writable directories via OS-level policies