CVE-2025-47287: Tornado vulnerable to excessive logging caused by malformed multipart form data
Summary
When Tornado's multipart/form-data parser encounters certain errors, it logs a warning but continues trying to parse the remainder of the data. This allows remote attackers to generate an extremely high volume of logs, constituting a DoS attack. This DoS is compounded by the fact that the logging subsystem is synchronous.
Affected versions
All versions of Tornado prior to 6.5 are affected. The vulnerable parser is enabled by default.
Solution
Upgrade to Tornado version 6.5. In the meantime, risk can be mitigated by blocking Content-Type: multipart/form-data in a proxy.
Other sources
Tornado is a Python web framework and asynchronous networking library. When Tornado's multipart/form-data parser encounters certain errors, it logs a warning but continues trying to parse the remainder of the data. This allows remote attackers to generate an extremely high volume of logs, constituting a DoS attack. This DoS is compounded by the fact that the logging subsystem is synchronous. All versions of Tornado prior to 6.5.0 are affected. The vulnerable parser is enabled by default. Upgrade to Tornado version 6.50 to receive a patch. As a workaround, risk can be mitigated by blocking Content-Type: multipart/form-data in a proxy.
— MITRE
Affected Software
Remediation
Event History
Frequently Asked Questions
What is the severity of CVE-2025-47287?
CVE-2025-47287 has been classified as a moderate severity vulnerability due to its potential to facilitate denial-of-service attacks.
How do I fix CVE-2025-47287?
To resolve CVE-2025-47287, you should upgrade to Tornado version 6.5.1 or later, which addresses the multipart/form-data parsing issue.
How does CVE-2025-47287 impact Tornado servers?
CVE-2025-47287 allows attackers to exploit Tornado servers by generating excessive logging, potentially leading to resource exhaustion.
What versions of Tornado are affected by CVE-2025-47287?
CVE-2025-47287 affects all versions of Tornado prior to 6.5.1.
Are there any workarounds for CVE-2025-47287?
There are no recommended workarounds for CVE-2025-47287; upgrading to a secure version is the best mitigation.