python-tornado — security advisory
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.
- Products
- python-tornado
- Affected versions
- 6.2.0-3, 6.2.0-3+deb12u1, 6.2.0-3+deb12u2, 6.2.0-3+deb12u3, 6.4.2-3, 6.4.2-3+deb13u1, 6.5.2-1, 6.5.2-2, 6.5.2-3
- Fixed versions
- 6.2.0-3+deb12u4, 6.4.2-3+deb13u2, 6.5.4-0.1
- CVEs
- CVE-2025-67726
- Confirmed fixed CVEs
- Not specified
- Updated in this feed
- 28 Oct 2026, 09:02 UTC · Revision 1
Source evidence
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.
osv:DEBIAN-CVE-2025-67726
python-tornado
Fixed versions: 6.2.0-3+deb12u4
python-tornado
Fixed versions: 6.4.2-3+deb13u2
python-tornado
Fixed versions: 6.5.4-0.1
Complete source record
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"url": "https://osv.dev/vulnerability/DEBIAN-CVE-2025-67726",
"method": "structured",
"payload": {
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"title": "DEBIAN-CVE-2025-67726",
"summary": "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.",
"evidence": "osv:DEBIAN-CVE-2025-67726",
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"modified": "2026-10-08T09:47:35.263236236Z",
"provider": "osv",
"upstream": [
"CVE-2025-67726"
],
"references": [
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]
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"related_cves": [
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"evidence": "/upstream"
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"security_relevant": true,
"severity_evidence": "/severity/0/score"
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"source_id": "core-osv",
"document_id": 98905,
"published_at": "2025-12-12T07:15:44.92+00:00"
}