GHSA-mhwm-jh88-3gjf
MEDIUMGHSA-mhwm-jh88-3gjf is a medium-severity (CVSS 4) CWE-1333 vulnerability in cgi. O3 Security confirms whether GHSA-mhwm-jh88-3gjf is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
CGI has Regular Expression Denial of Service (ReDoS) potential in Util#escapeElement
Blast Radius
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Description
There is a possibility for Regular expression Denial of Service (ReDoS) by in the cgi gem. This vulnerability has been assigned the CVE identifier CVE-2025-27220. We recommend upgrading the cgi gem.
Details
The regular expression used in CGI::Util#escapeElement is vulnerable to ReDoS. The crafted input could lead to a high CPU consumption.
This vulnerability only affects Ruby 3.1 and 3.2. If you are using these versions, please update CGI gem to version 0.3.5.1, 0.3.7, 0.4.2 or later.
Affected versions
cgi gem versions <= 0.3.5, 0.3.6, 0.4.0 and 0.4.1.
Credits
Thanks to svalkanov for discovering this issue. Also thanks to nobu for fixing this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | cgi | all versions | 0.3.5.1 |
| 💎RubyGems | cgi | ≥ 0.3.6&&< 0.3.7 | 0.3.7 |
| 💎RubyGems | cgi | ≥ 0.4.0&&< 0.4.2 | 0.4.2 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for cgi. 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 cgi to 0.3.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-mhwm-jh88-3gjf 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 GHSA-mhwm-jh88-3gjf 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 GHSA-mhwm-jh88-3gjf. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-mhwm-jh88-3gjf in your dependencies?
O3 detects GHSA-mhwm-jh88-3gjf across RubyGems dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.