CVE-2025-67726 is a high-severity (CVSS 7.5) Uncontrolled Resource Consumption vulnerability in tornado. O3 Security confirms whether CVE-2025-67726 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- 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-2025-67726.
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-2025-67726 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 369,023 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
tornadoReal-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
Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request with a large number of maliciously crafted parameters in a Content-Disposition header, the server's CPU usage increases quadratically (O(n²)) during parsing. Due to Tornado's single event loop architecture, a single malicious request can cause the entire server to become unresponsive for an extended period. This issue is fixed in version 6.5.3.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | tornado | all versions | 6.5.3 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for tornado. 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 tornado to 6.5.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-67726 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-2025-67726 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-2025-67726. 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 availability impact of this flaw is partially mitigated on Red Hat products as the host systems are not at risk.
Frequently Asked Questions
Is CVE-2025-67726 in your dependencies?
O3 detects CVE-2025-67726 across PyPI dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.