GHSA-jhmp-mqwm-3gq8: Tornado: Quadratic DoS via Crafted Multipart Parameters
Summary
The _parseparam function in Tornado's httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data. This function uses an inefficient algorithm that repeatedly calls string.count() within a nested loop while processing quoted semicolons (e.g., param=";").
As a result, 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, leading to a Denial of Service (DoS).
Severity: High
Details
Original advisory: https://github.com/advisories/GHSA-jhmp-mqwm-3gq8
Exploitation outlook
EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.
- Low exploitation riskCVE-2025-677260.51% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 41% of all scored CVEs.
Referenced CVEs
| CVE | CSIRTS overview | External |
|---|---|---|
| CVE-2025-67726 | coverage & exploitation status | NVD · CVE.org |
Same CVEs, other sources
How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.
- unknownMultiple vulnerabilities in IBM products (July 17, 2026)cert-fr-avis
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