Vulnerability Details CVE-2025-67726
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.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 22.4%
CVSS Severity
CVSS v3 Score 7.5
References
Products affected by CVE-2025-67726
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cpe:2.3:a:tornadoweb:tornado:1.0
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cpe:2.3:a:tornadoweb:tornado:1.0.1
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cpe:2.3:a:tornadoweb:tornado:1.1
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cpe:2.3:a:tornadoweb:tornado:1.1.1
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cpe:2.3:a:tornadoweb:tornado:1.2
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cpe:2.3:a:tornadoweb:tornado:1.2.1
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cpe:2.3:a:tornadoweb:tornado:2.0
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cpe:2.3:a:tornadoweb:tornado:2.1
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cpe:2.3:a:tornadoweb:tornado:2.1.1
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cpe:2.3:a:tornadoweb:tornado:2.2
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cpe:2.3:a:tornadoweb:tornado:2.2.1
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cpe:2.3:a:tornadoweb:tornado:2.3.0
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cpe:2.3:a:tornadoweb:tornado:2.4.0
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cpe:2.3:a:tornadoweb:tornado:2.4.1
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cpe:2.3:a:tornadoweb:tornado:3.0.0
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cpe:2.3:a:tornadoweb:tornado:3.0.1
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cpe:2.3:a:tornadoweb:tornado:3.0.2
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cpe:2.3:a:tornadoweb:tornado:3.1.0
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cpe:2.3:a:tornadoweb:tornado:3.1.1
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cpe:2.3:a:tornadoweb:tornado:3.2.0
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cpe:2.3:a:tornadoweb:tornado:3.2.1
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cpe:2.3:a:tornadoweb:tornado:3.2.2
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cpe:2.3:a:tornadoweb:tornado:4.0.0
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cpe:2.3:a:tornadoweb:tornado:4.0.1
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cpe:2.3:a:tornadoweb:tornado:4.0.2
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cpe:2.3:a:tornadoweb:tornado:4.1.0
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cpe:2.3:a:tornadoweb:tornado:4.2.0
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cpe:2.3:a:tornadoweb:tornado:4.2.1
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cpe:2.3:a:tornadoweb:tornado:4.3.0
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cpe:2.3:a:tornadoweb:tornado:4.4.0
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cpe:2.3:a:tornadoweb:tornado:4.4.1
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cpe:2.3:a:tornadoweb:tornado:4.4.2
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cpe:2.3:a:tornadoweb:tornado:4.4.3
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cpe:2.3:a:tornadoweb:tornado:4.5.0
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cpe:2.3:a:tornadoweb:tornado:4.5.1
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cpe:2.3:a:tornadoweb:tornado:4.5.2
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cpe:2.3:a:tornadoweb:tornado:4.5.3
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cpe:2.3:a:tornadoweb:tornado:5.0.0
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cpe:2.3:a:tornadoweb:tornado:5.0.1
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cpe:2.3:a:tornadoweb:tornado:5.0.2
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cpe:2.3:a:tornadoweb:tornado:5.1.0
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cpe:2.3:a:tornadoweb:tornado:5.1.1
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cpe:2.3:a:tornadoweb:tornado:6.0.0
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cpe:2.3:a:tornadoweb:tornado:6.0.1
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cpe:2.3:a:tornadoweb:tornado:6.0.2
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cpe:2.3:a:tornadoweb:tornado:6.0.3