CVE-2025-27219 is a medium-severity (CVSS 5.8) CWE-770 vulnerability in cgi. A fix is available for cgi — see the affected versions and patch details below.
CGI has Denial of Service (DoS) potential in Cookie.parse
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2025-27219.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2025-27219 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
cgi💎cgi💎cgiReal-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
There is a possibility for DoS by in the cgi gem. This vulnerability has been assigned the CVE identifier CVE-2025-27219. We recommend upgrading the cgi gem.
Details
CGI::Cookie.parse took super-linear time to parse a cookie string in some cases. Feeding a maliciously crafted cookie string into the method could lead to a Denial of Service.
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 lio346 for discovering this issue. Also thanks to mame for fixing this vulnerability.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | cgi | all versions | 0.3.5.1bundle update cgi --conservative |
| 💎RubyGems | cgi | ≥ 0.3.6&&< 0.3.7 | 0.3.7bundle update cgi --conservative |
| 💎RubyGems | cgi | ≥ 0.4.0&&< 0.4.2 | 0.4.2bundle update cgi --conservative |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for cgi, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update cgi to 0.3.5.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-27219 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 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2025-27219 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2025-27219. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This issue will cause an excessive resource consumption, potentially resulting in a bad application performance. However, an attacker does have the ability to completely deny service to legitimate users. For this reason, this vulnerability has been rated with a moderate severity.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Enterprise Linux 10 | ruby-0:3.3.8-10.el10_0 | RHSA-2025:8131 |
| Red Hat Enterprise Linux 8 | ruby:3.3-8100020250414172630.489197e6 | RHSA-2025:10217 |
| Red Hat Enterprise Linux 8 | ruby:3.1-8100020250407112943.489197e6 | RHSA-2025:4063 |
| Red Hat Enterprise Linux 9 | ruby-0:3.0.7-165.el9_5 | RHSA-2025:4487 |
| Red Hat Enterprise Linux 9 | ruby:3.1-9050020250404144903.9 | RHSA-2025:4488 |
| Red Hat Enterprise Linux 9 | ruby:3.3-9050020250415095239.9 | RHSA-2025:4493 |
Frequently Asked Questions
Is CVE-2025-27219 in your dependencies?
O3 Security finds CVE-2025-27219 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.