CVE-2025-67726
Tornado is a Python web framework and asynchronous networking library.
Impact
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 | Affected | Fixed in |
|---|---|---|---|
| pip | tornado | < 6.5.3 | 6.5.3 |
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| Tornadoweb | Tornado | before 6.5.3 |
Weakness classification
References
- NVD record
- CVE.org record
- GitHub advisory
- https://github.com/advisories/GHSA-jhmp-mqwm-3gq8
- https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8
- https://nvd.nist.gov/vuln/detail/CVE-2025-67726
- https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
- https://github.com/pypa/advisory-database/tree/main/vulns/tornado/PYSEC-2025-267.yaml
- https://github.com/tornadoweb/tornado/releases/tag/v6.5.3