PYSEC-2025-266
See a problem?- Import Source
- https://github.com/pypa/advisory-database/blob/main/vulns/tornado/PYSEC-2025-266.yaml
- JSON Data
- https://api.osv.dev/v1/vulns/PYSEC-2025-266
- Aliases
-
- CVE-2025-67725
- GHSA-c98p-7wgm-6p64
- Published
- 2025-12-12T06:15:41.380Z
- Modified
- 2026-07-13T07:15:44.064352714Z
- Severity
-
- 7.5 (High) CVSS_V3 - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CVSS Calculator
- Summary
- [none]
- Details
-
Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. The function accumulates values using string concatenation when the same header name is repeated, causing a Denial of Service (DoS). Due to Python string immutability, each concatenation copies the entire string, resulting in O(n²) time complexity. The severity can vary from high if maxheadersize has been increased from its default, to low if it has its default value of 64KB. This issue is fixed in version 6.5.3.
- References
Affected packages
PyPI / tornado
Package
- Name
- tornado
- View open source insights on deps.dev
- Purl
- pkg:pypi/tornado
Affected ranges
- Type
- ECOSYSTEM
- Events
-
Introduced0Unknown introduced version / All previous versions are affectedFixed6.5.3
Affected versions
0.*
0.2
1.*
1.0
1.1
1.1.1
1.2
1.2.1
2.*
2.0
2.1
2.1.1
2.2
2.2.1
2.3
2.4
2.4.1
3.*
3.0
3.0.1
3.0.2
3.1
3.1.1
3.2
3.2.1
3.2.2
4.*
4.0
4.0.1
4.0.2
4.1b2
4.1
4.2b1
4.2
4.2.1
4.3b1
4.3b2
4.3
4.4b1
4.4
4.4.1
4.4.2
4.4.3
4.5b1
4.5b2
4.5
4.5.1
4.5.2
4.5.3
5.*
5.0a1
5.0b1
5.0
5.0.1
5.0.2
5.1b1
5.1
5.1.1
6.*
6.0a1
6.0b1
6.0
6.0.1
6.0.2
6.0.3
6.0.4
6.1b1
6.1b2
6.1
6.2b1
6.2b2
6.2
6.3b1
6.3
6.3.1
6.3.2
6.3.3
6.4b1
6.4
6.4.1
6.4.2
6.5b1
6.5
6.5.1
6.5.2