VDB
DEBIAN-CVE-2025-67725
DEBIAN-CVE-2025-67725
PUBLISHED
CVSS 7.5 HIGH
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 max_header_size 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.
Risk Scores
CVSS v3.1
7.5
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Debian:11 | python-tornado | 6.1.0-1, 6.1.0-1, 0 |
| Debian:14 | python-tornado | 6.4.2-3, 6.5.2-2, 6.5.2-1 |
| Debian:13 | python-tornado | 6.4.2-3, 0, 6.4.2-3 |
| Debian:12 | python-tornado | *, 6.2.0-3+deb12u2, 6.2.0-3+deb12u1 |
Timeline
- Dec 12, 2025 CVE Published
- Apr 28, 2026 CVE Updated