How severe is CVE-2021-21289?

CVE-2021-21289 has a CVSS score of 8.3/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-21289?

CVE-2021-21289 affects the following packages: mechanize (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2021-21289?

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.

How do I detect CVE-2021-21289 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mechanize, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-21289 if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is CVE-2021-21289 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-21289 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-21289?

CVE-2021-21289 has an EPSS (Exploit Prediction Scoring System) score of 3.5%, placing it in the 89th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-21289?

CVE-2021-21289 is classified as OS Command Injection (CWE-78). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-21289 published, and has it been updated?

CVE-2021-21289 was published on February 2, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

💎

💎 RubyGems

Not in CISA KEV

HIGH severity

CVE-2021-21289 — mechanize

HIGHFix: sparklemotion/mechanize@66a6a1b

CVE-2021-21289 is a high-severity (CVSS 8.3) OS Command Injection vulnerability in mechanize. A fix is available for mechanize — see the affected versions and patch details below.

Command Injection Vulnerability in Mechanize

Also known asGHSA-qrqm-fpv6-6r8g

Published

Feb 2, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 4, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

3.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs89th percentile — riskier than 89% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

💎mechanize

Real-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

This security advisory has been created for public disclosure of a Command Injection vulnerability that was responsibly reported by @kyoshidajp (Katsuhiko YOSHIDA).

Impact

Mechanize >= v2.0, < v2.7.7 allows 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: since v2.0 (see 208e3ed)
Mechanize::CookieJar#save_as: since v2.0 (see 5b776a4)
Mechanize#download: since v2.2 (see dc91667)
Mechanize::Download#save and #save! since v2.1 (see 98b2f51, bd62ff0)
Mechanize::File#save and #save_as: since v2.1 (see 2bf7519)
Mechanize::FileResponse#read_body: since v2.0 (see 01039f5)

Patches

These vulnerabilities are patched in Mechanize v2.7.7.

Workarounds

No workarounds are available. We recommend upgrading to v2.7.7 or later.

References

See https://docs.rubocop.org/rubocop/cops_security.html#securityopen for background on why Kernel.open should not be used with untrusted input.

For more information

If you have any questions or comments about this advisory, please open an issue in sparklemotion/mechanize.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`mechanize`	≥ 2.0.0&&< 2.7.7	2.7.7`bundle update mechanize --conservative`

Affected Products

3 products · 4 configurations

debian linuxdebian

1 version

9.0

fedorafedoraproject

2 versions

3233

Application

mechanizemechanize_project

≥ 2.0 && < 2.7.7

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for mechanize, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Frequently Asked Questions

This security advisory has been created for public disclosure of a Command Injection vulnerability that was responsibly reported by @kyoshidajp (Katsuhiko YOSHIDA). ### Impact Mechanize `>= v2.0`, `< v2.7.7` allows 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`: since v2.0 (see 208e3ed) - `Mechanize::CookieJar#save_as`: since v2.0 (see 5b776a4) - `Mechanize#download`: since v2.2 (see dc91