Waitress version 1.4.2 allows a DOS attack When waitress receives a header that contains invalid characters. When a header like Bad-header: xxxxxxxxxxxxxxxx10 is received, it will cause the regular expression engine to catastrophically backtrack causing the process to use 100% CPU time and blocking any other interactions. This allows an attacker to send a single request with an invalid header and take the service offline. This issue was introduced in version 1.4.2 when the regular expression was updated to attempt to match the behaviour required by errata associated with RFC7230. The regular expression that is used to validate incoming headers has been updated in version 1.4.3, it is recommended that people upgrade to the new version of Waitress as soon as possible.
The product does not properly control the allocation and maintenance of a limited resource.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Waitress | Agendaless | 1.4.2 (including) | 1.4.2 (including) |
| Waitress | Ubuntu | trusty | * |
Mitigation of resource exhaustion attacks requires that the target system either:
The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question.
The second solution is simply difficult to effectively institute – and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.