Grackle is a GraphQL server written in functional Scala, built on the Typelevel stack. The GraphQL specification requires that GraphQL fragments must not form cycles, either directly or indirectly. Prior to Grackle version 0.18.0, that requirement wasnt checked, and queries with cyclic fragments would have been accepted for type checking and compilation. The attempted compilation of such fragments would result in a JVM StackOverflowError being thrown. Some knowledge of an applications GraphQL schema would be required to construct such a query, however no knowledge of any application-specific performance or other behavioural characteristics would be needed.
Grackle uses the cats-parse library for parsing GraphQL queries. Prior to version 0.18.0, Grackle made use of the cats-parse recursive operator. However, recursive is not currently stack safe. recursive was used in three places in the parser: nested selection sets, nested input values (lists and objects), and nested list type declarations. Consequently, queries with deeply nested selection sets, input values or list types could be constructed which exploited this, causing a JVM StackOverflowException to be thrown during parsing. Because this happens very early in query processing, no specific knowledge of an applications GraphQL schema would be required to construct such a query.
The possibility of small queries resulting in stack overflow is a potential denial of service vulnerability. This potentially affects all applications using Grackle which have untrusted users. Both stack overflow issues have been resolved in the v0.18.0 release of Grackle. As a workaround, users could interpose a sanitizing layer in between untrusted input and Grackle query processing.
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.
| Name | Vendor | Start Version | End Version |
|---|---|---|---|
| Grackle | Typelevel | * | 0.18.0 (excluding) |
Limited resources include memory, file system storage, database connection pool entries, and CPU. If an attacker can trigger the allocation of these limited resources, but the number or size of the resources is not controlled, then the attacker could cause a denial of service that consumes all available resources. This would prevent valid users from accessing the product, and it could potentially have an impact on the surrounding environment. For example, a memory exhaustion attack against an application could slow down the application as well as its host operating system. There are at least three distinct scenarios which can commonly lead to resource exhaustion:
Resource exhaustion problems are often result due to an incorrect implementation of the following situations:
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.