tornadoweb tornado up to 6.5.2 HTTP HTTPHeaders.add resource consumption

Summaryinfo

A vulnerability was found in tornadoweb tornado up to 6.5.2. It has been classified as problematic. The affected element is the function HTTPHeaders.add of the component HTTP Handler. The manipulation leads to resource consumption. This vulnerability is traded as CVE-2025-67725. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in tornadoweb tornado up to 6.5.2. This issue affects the function HTTPHeaders.add of the component HTTP Handler. The manipulation with an unknown input leads to a resource consumption vulnerability. Using CWE to declare the problem leads to CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. Impacted is availability. The summary by CVE is:

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.

The advisory is shared at github.com. The identification of this vulnerability is CVE-2025-67725 since 12/10/2025. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 278568 (Linux Distros Unpatched Vulnerability : CVE-2025-67725), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 6.5.3 eliminates this vulnerability.

The vulnerability is also documented in the databases at Tenable (278568) and CERT Bund (WID-SEC-2026-0195). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• SUSE Linux
• Oracle Linux
• RESF Rocky Linux
• Red Hat Enterprise Linux

Productinfo

Vendor

• tornadoweb

Name

• tornado

Version

• 6.5.0
• 6.5.1
• 6.5.2

Website

• Product: https://github.com/tornadoweb/tornado/

CPE 2.3info

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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