AutoMapper Vulnerable to Denial of Service (DoS) via Uncontrolled Recursion

AutoMapper is a convention-based object-object mapper in .NET. Versions prior to 15.1.1 and 16.1.1 are vulnerable to a Denial of Service (DoS) attack. When mapping deeply nested object graphs, the library uses recursive method calls without enforcing a default maximum depth limit. This allows an attacker to provide a specially crafted object graph that exhausts the thread's stack memory, triggering a `StackOverflowException` and causing the entire application process to terminate. Versions 15.1.1 and 16.1.1 fix the issue.

AutoMapper is a convention-based object-object mapper in .NET. Versions prior to 15.1.1 and 16.1.1 are vulnerable to a Denial of Service (DoS) attack. When mapping deeply nested object graphs, the library uses recursive method calls without enforcing a default maximum depth limit. This allows an attacker to provide a specially crafted object graph that exhausts the thread's stack memory, triggering a `StackOverflowException` and causing the entire application process to terminate. Versions 15.1.1 and 16.1.1 fix the issue.

AutoMapper is a convention-based object-object mapper in .NET. Versions prior to 15.1.1 and 16.1.1 are vulnerable to a Denial of Service (DoS) attack. When mapping deeply nested object graphs, the library uses recursive method calls without enforcing a default maximum depth limit. This allows an attacker to provide a specially crafted object graph that exhausts the thread's stack memory, triggering a `StackOverflowException` and causing the entire application process to terminate. Versions 15.1.1 and 16.1.1 fix the issue.

### Summary AutoMapper is vulnerable to a Denial of Service (DoS) attack. When mapping deeply nested object graphs, the library uses recursive method calls without enforcing a default maximum depth limit. This allows an attacker to provide a specially crafted object graph that exhausts the thread's stack memory, triggering a `StackOverflowException` and causing the entire application process to terminate. ### Description The vulnerability exists in the core mapping engine. When a source object contains a property of the same type (or a type that eventually points back to itself), AutoMapper recursively attempts to map each level. Because there is no default limit on how many levels deep this recursion can go, a sufficiently nested object (approximately 25,000+ levels in standard .NET environments) will exceed the stack size. Since `StackOverflowException` cannot be caught in modern .NET runtimes, the application cannot recover and will crash immediately. ### Impact * **Availability:** An attacker can crash the application server, leading to a complete Denial of Service. * **Process Termination:** Unlike standard exceptions, this terminates the entire process, not just the individual request thread. ### Proof of Concept (PoC) The following C# code demonstrates the crash by creating a nested "Circular" object graph and attempting to map it: ```csharp class Circular { public Circular Self { get; set; } } // Setup configuration var config = new MapperConfiguration(cfg => { cfg.CreateMap<Circular, Circular>(); }); var mapper = config.CreateMapper(); // Create a deeply nested object (28,000+ levels) var root = new Circular(); var current = root; for (int i = 0; i < 30000; i++) { current.Self = new Circular(); current = current.Self; } // This call triggers the StackOverflowException and crashes the process mapper.Map<Circular>(root); ``` ### Recommended Mitigation 1. **Secure Defaults:** Implement a default `MaxDepth` (e.g., 32 or 64) for all mapping operations. 2. **Configurable Limit:** Allow users to increase this limit if necessary, but ensure it is enabled by default to protect unsuspecting developers.