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:
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
- Secure Defaults: Implement a default
MaxDepth (e.g., 32 or 64) for all mapping operations.
- Configurable Limit: Allow users to increase this limit if necessary, but ensure it is enabled by default to protect unsuspecting developers.
References
skdishansachin Finder
jbogard Remediation developer
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
StackOverflowExceptionand 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
StackOverflowExceptioncannot be caught in modern .NET runtimes, the application cannot recover and will crash immediately.Impact
Proof of Concept (PoC)
The following C# code demonstrates the crash by creating a nested "Circular" object graph and attempting to map it:
Recommended Mitigation
MaxDepth(e.g., 32 or 64) for all mapping operations.References