Vulnerability · Published Dec 12, 2025 · Assigned by GitHub_M
CVE-2025-67726Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
High 7.5
In plain English
A high-severity uncontrolled resource consumption in tornado from tornadoweb. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 45% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official 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 & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:8 | pcs | 0.10.18-2.el8_10.8.alma.1 | ALSA-2026:0930 |
| AlmaLinux:8 | pcs-snmp | 0.10.18-2.el8_10.8.alma.1 | ALSA-2026:0930 |
| Alpine:v3.23 | py3-tornado | 6.5.4-r0 | ALPINE-CVE-2025-67726 |
| Alpine:v3.24 | py3-tornado | 6.5.4-r0 | ALPINE-CVE-2025-67726 |
| Debian:12 | python-tornado | 6.2.0-3+deb12u4 | DEBIAN-CVE-2025-67726 |
| Debian:13 | python-tornado | 6.4.2-3+deb13u2 | DEBIAN-CVE-2025-67726 |
| Debian:14 | python-tornado | 6.5.4-0.1 | DEBIAN-CVE-2025-67726 |
| PyPI | tornado | 6.5.3 | PYSEC-2025-267 |
| PyPI | tornado | 6.5.3 | GHSA-jhmp-mqwm-3gq8 |
| Rocky Linux:8 | pcs | 0:0.10.18-2.el8_10.8 | RLSA-2026:0930 |
| Ubuntu:24.04:LTS | python-tornado | 6.4.0-1ubuntu0.4 | UBUNTU-CVE-2025-67726 |
| Ubuntu:25.10 | python-tornado | 6.4.2-3ubuntu0.2 | UBUNTU-CVE-2025-67726 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| tornadoweb | tornado | < 6.5.3 |
Weakness: CWE-834, CWE-400 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H