CVE-2024-3651 is a medium-severity (CVSS 6.2) CWE-1333 vulnerability in idna. 1 public exploit reference exists, so weaponization risk is real. A fix is available for idna — see the affected versions and patch details below.
Denial of Service via Quadratic Complexity in kjd/idna
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-2024-3651.
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-2024-3651 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 378,567 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
idnaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Impact
A specially crafted argument to the idna.encode() function could consume significant resources. This may lead to a denial-of-service.
Patches
The function has been refined to reject such strings without the associated resource consumption in version 3.7.
Workarounds
Domain names cannot exceed 253 characters in length, if this length limit is enforced prior to passing the domain to the idna.encode() function it should no longer consume significant resources. This is triggered by arbitrarily large inputs that would not occur in normal usage, but may be passed to the library assuming there is no preliminary input validation by the higher-level application.
References
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | idna | all versions | 3.7pip install --upgrade 'idna==3.7' |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for idna, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update idna to 3.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-3651 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-2024-3651 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2024-3651. 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.
The vulnerability in the idna.encode() function, allowing for resource consumption via specially crafted arguments, is categorized as a moderate severity issue due to its potential impact on system availability rather than data integrity or confidentiality. While the vulnerability can lead to a denial-of-service…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Ansible Automation Platform 2.4 for RHEL 8 | python3x-idna-0:3.7-1.el8ap | RHSA-2024:3781 |
| Red Hat Enterprise Linux 7 Extended Lifecycle Support | python-idna-0:2.4-2.el7_9 | RHSA-2024:8365 |
| Red Hat Enterprise Linux 8 | python39:3.9-8100020240516111311.d47b87a4 | RHSA-2024:3466 |
| Red Hat Enterprise Linux 8 | python-idna-0:2.5-7.el8_10 | RHSA-2024:4260 |
| Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support | python-idna-0:2.5-5.el8_6.1 | RHSA-2024:3552 |
| Red Hat Enterprise Linux 8.8 Extended Update Support | python-idna-0:2.5-5.el8_8.1 | RHSA-2024:3543 |
| Red Hat Enterprise Linux 9 | python-idna-0:2.10-7.el9_4.1 | RHSA-2024:3846 |
Frequently Asked Questions
Is CVE-2024-3651 in your dependencies?
O3 Security finds CVE-2024-3651 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.