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Uncontrolled Resource Consumption

CVE-2025-67725

High
7.5/10

Summary

Tornado is a Python web framework and asynchronous networking library. In versions through 6.5.2, 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(n) 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.

  • LOW
  • NETWORK
  • NONE
  • UNCHANGED
  • NONE
  • NONE
  • NONE
  • HIGH

CWE-400 - Uncontrolled resource consumption

An uncontrolled resource allocation attack (also known as resource exhaustion attack) triggers unauthorized overconsumption of the limited resources in an application, such as memory, file system storage, database connection pool entries, and CPU. This may lead to denial of service for valid users and degradation of the application's functionality as well as that of the host operating system.

References

Advisory Timeline

  • Published