CVE-2021-21289
HIGHCVE-2021-21289 is a high-severity (CVSS 8.3) OS Command Injection vulnerability in mechanize. O3 Security confirms whether CVE-2021-21289 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Command Injection Vulnerability in Mechanize
Blast Radius
mechanizeReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
Description
Mechanize is an open-source ruby library that makes automated web interaction easy. In Mechanize from version 2.0.0 and before version 2.7.7 there is a command injection vulnerability. Affected versions of mechanize allow for OS commands to be injected using several classes' methods which implicitly use Ruby's Kernel.open method. Exploitation is possible only if untrusted input is used as a local filename and passed to any of these calls: Mechanize::CookieJar#load, Mechanize::CookieJar#save_as, Mechanize#download, Mechanize::Download#save, Mechanize::File#save, and Mechanize::FileResponse#read_body. This is fixed in version 2.7.7.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | mechanize | ≥ 2.0.0&&< 2.7.7 | 2.7.7 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mechanize. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update mechanize to 2.7.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21289 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-21289 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2021-21289. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2021-21289 in your dependencies?
O3 detects CVE-2021-21289 across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.