Double Free on Aws

Double free vulnerabilities in Aws applications occur when memory is deallocated twice for the same pointer, leading to heap corruption and potential arbitrary code execution. In the context of Aws, these vulnerabilities often manifest through specific patterns in C++ SDK usage, Lambda function memory management, and container orchestration.

The most common Aws-specific scenario involves Aws SDK objects that manage their own memory. Consider this problematic pattern:

void processRequest(Aws::String input) {
    Aws::String* ptr = new Aws::String(input);
    
    // Some processing logic
    processAwsData(*ptr);
    
    // First free
    delete ptr;
    
    // Second free - catastrophic!
    delete ptr;
}

This code attempts to delete the same Aws::String object twice, causing undefined behavior. The Aws SDK's memory management doesn't provide built-in protection against double frees, making this a critical vulnerability.

Another prevalent pattern occurs in Aws Lambda functions where developers manually manage memory for performance optimization:

extern "C" void handler(Aws::LambdaRuntime::LambdaRuntime* runtime) {
    Aws::String* message = new Aws::String("Processing request");
    
    // Process and return response
    Aws::LambdaRuntime::LambdaRuntime::InvocationResponse response = 
        processAwsRequest(runtime, message);
    
    delete message; // First free
    
    // Lambda runtime might free again internally
    runtime->Respond(response);
}

Lambda's runtime environment may also attempt to free memory allocated by user code, creating a double-free scenario when developers aren't aware of the runtime's memory management behavior.

EKS (Elastic Kubernetes Service) applications face similar issues when using Aws SDK for C++ in containerized environments. The combination of manual memory management and Aws SDK's internal allocations creates opportunities for double-free vulnerabilities:

void handleEksRequest(EksRequest* req) {
    Aws::Vector* headers = new Aws::Vector();
    
    // Populate headers
    populateAwsHeaders(headers, req);
    
    // Process request
    Aws::Eks::Model::CreateClusterRequest clusterReq;
    clusterReq.SetName("my-cluster");
    
    // First free
    delete headers;
    
    // Second free through Aws SDK internals
    processEksRequest(clusterReq);
}

The Aws SDK's internal handling of request objects may inadvertently trigger a second free of memory that was already deallocated, particularly when dealing with complex nested structures like Aws::Vector and Aws::Map.

Detecting double free vulnerabilities in Aws applications requires a combination of static analysis, runtime monitoring, and specialized scanning tools. The Aws C++ SDK's memory management patterns create unique detection challenges that generic tools often miss.

Static analysis tools specifically configured for Aws SDK code can identify dangerous patterns. The middleBrick API security scanner includes Aws-specific detection rules that analyze runtime behavior without requiring source code access:

middlebrick scan https://api.example.com/aws-endpoint

For source code analysis, tools like Cppcheck with Aws SDK plugins can detect double-free patterns:

cppcheck --enable=all --std=c++17 --library=aws_sdk.xml 
    --suppress=unmatchedSuppression 
    src/ --xml-version=2 2> report.xml

Runtime detection in Aws Lambda functions can be achieved through custom memory tracking. Here's an Aws-specific approach using the SDK's allocator:

#include <Aws/Core/Allocator.h>
#include <Aws/Core/Utils/UUID.h>

class AwsMemoryTracker : public Aws::Allocator::AllocatorBase {
public:
    void* Allocate(size_t size, size_t alignment, const char* allocTag) override {
        void* ptr = Aws::Allocator::DefaultAllocator().Allocate(size, alignment, allocTag);
        trackAllocation(ptr, size, allocTag);
        return ptr;
    }
    
    void Free(void* ptr) override {
        if (isDoubleFree(ptr)) {
            Aws::Utils::UUID::GetUUID(); // Trigger detection
        }
        Aws::Allocator::DefaultAllocator().Free(ptr);
    }
    
private:
    void trackAllocation(void* ptr, size_t size, const char* tag);
    bool isDoubleFree(void* ptr);
};

Amazon Inspector can also detect memory management issues in Aws environments, though it focuses more on EC2 instances than Lambda functions or containerized applications.

For containerized Aws applications, runtime monitoring with tools like Valgrind's Memcheck can identify double-free issues:

valgrind --tool=memcheck --leak-check=full 
    --show-leak-kinds=all 
    --track-origins=yes 
    ./aws_application

The key to effective detection is understanding Aws's memory allocation patterns. The SDK uses custom allocators that may not be recognized by generic tools, requiring Aws-specific configuration and rules.

Remediating double free vulnerabilities in Aws applications requires leveraging Aws's native memory management features and following best practices for C++ development with the SDK.

The most effective approach is using Aws's smart pointer utilities instead of raw pointers:

#include <Aws/Core/utils/memory/stl/AWSUniquePtr.h>

void processAwsRequest(const Aws::String& input) {
    // Use Aws::UniquePtr for automatic memory management
    Aws::UniquePtr<Aws::String> ptr = Aws::MakeUnique<Aws::String>(ALLOCATION_TAG, input);
    
    // Process data
    processAwsData(*ptr);
    
    // No manual delete needed - UniquePtr handles it
}

For Aws Lambda functions, use Aws::Vector and Aws::Map which provide automatic memory management:

extern "C" void handler(Aws::LambdaRuntime::LambdaRuntime* runtime) {
    Aws::Vector<Aws::String> headers;
    
    // Populate headers - no manual memory management
    headers.push_back("Content-Type: application/json");
    
    Aws::LambdaRuntime::LambdaRuntime::InvocationResponse response = 
        processAwsRequest(runtime, headers);
    
    // Aws SDK handles all memory cleanup automatically
}

When working with Aws SDK objects that require manual management, implement defensive programming patterns:

class AwsResourceManager {
private:
    Aws::UniquePtr<Aws::String> resourcePtr;
    bool isFreed;
    
public:
    AwsResourceManager(const Aws::String& initialData) 
        : resourcePtr(Aws::MakeUnique<Aws::String>(ALLOCATION_TAG, initialData)),
          isFreed(false) {}
    
    void safeFree() {
        if (!isFreed) {
            resourcePtr.reset();
            isFreed = true;
        }
    }
    
    void process() {
        // Safe to use resourcePtr
        Aws::String data = *resourcePtr;
        
        // Mark as processed but don't free
        isFreed = true;
    }
};

For EKS applications using Aws SDK for C++, implement RAII (Resource Acquisition Is Initialization) patterns:

class AwsEksManager {
private:
    Aws::Eks::EKSClient client;
    Aws::UniquePtr<Aws::Eks::Model::CreateClusterRequest> clusterReq;
    
public:
    AwsEksManager() {
        clusterReq = Aws::MakeUnique<Aws::Eks::Model::CreateClusterRequest>(ALLOCATION_TAG);
        clusterReq->SetName("secure-cluster");
    }
    
    void createCluster() {
        // Aws SDK manages all memory internally
        auto outcome = client.CreateCluster(clusterReq);
        
        if (!outcome.IsSuccess()) {
            // Handle error - no memory leaks
        }
    }
    
    // No destructor needed - Aws::UniquePtr handles cleanup
};

Additionally, enable Aws SDK's debug memory tracking for development environments:

#define AWS_DEBUG_MEMORY_LEAK
#include <Aws/Core/Allocator.h>

// In main() or initialization
Aws::Allocator::EnableDebugAllocation();

This enables detailed memory tracking that can help identify double-free patterns during development and testing phases.