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 6.5.0 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.
Summary
When Tornado's
multipart/form-dataparser 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 6.5.0 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-datain a proxy.