CVE-2025-67726: high-severity vulnerability in tornadoweb tornado
Tornado is Vulnerable to Quadratic DoS via Crafted Multipart Parameters
Published · Updated
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21Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 7.5epss 0.5%
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected products
tornadoweb · tornadoRelated CVEs — tornadoweb tornado
In the same product, most dangerous first.
CVE-2024-52804HIGHTornado has HTTP cookie parsing DoS vulnerabilityEPSS 1.0%CVE-2025-47287HIGHTornado vulnerable to excessive logging caused by malformed multipart form dataEPSS 0.7%CVE-2026-103262HIGHTornado before 6.5.9 Denial of Service via CurlAsyncHTTPClientEPSS 0.6%CVE-2026-49855HIGHtornado AsyncHTTPClient accumulates decompressed chunks without size limit (gzip bomb)EPSS 0.6%CVE-2025-67725HIGHTornado is Vulnerable to Quadratic DoS via Repeated Header CoalescingEPSS 0.6%CVE-2026-103263HIGHTornado before 6.5.9 StaticFileHandler Path Traversal via SymlinkEPSS 0.5%