Google V8 computes hash values for form parameters without restricting the ability to trigger hash collisions predictably, which allows remote attackers to cause a denial of service (CPU consumption) by sending many crafted parameters, as demonstrated by attacks against Node.js.
CVE-2011-5037 exposes a critical vulnerability in Google V8's hash function, enabling denial-of-service (DoS) attacks. Attackers can craft malicious input to trigger hash collisions, leading to excessive CPU consumption and service unavailability. This vulnerability primarily impacts applications built on JavaScript engines, such as Node.js, making them susceptible to remote exploitation.
Step 1: Payload Generation: The attacker crafts a large number of HTTP form parameters. These parameters are designed to collide within the V8 hash function, meaning they all generate the same hash value. This is achieved by carefully selecting the parameter keys or values, depending on the hash function's implementation.
Step 2: Payload Delivery: The attacker sends the crafted HTTP request containing the malicious parameters to the vulnerable application (e.g., a Node.js server).
Step 3: Parameter Parsing: The application's JavaScript engine (V8) parses the incoming HTTP request and extracts the form parameters.
Step 4: Hash Table Insertion: The V8 engine attempts to insert the parameters into an internal hash table, using the vulnerable hash function to compute the hash keys.
Step 5: Collision Triggering: Due to the crafted parameters, a large number of collisions occur within the hash table. This forces the engine to perform inefficient operations (e.g., linear probing or chaining) to resolve the collisions.
Step 6: CPU Exhaustion: The repeated collision resolution consumes significant CPU resources, leading to a denial-of-service condition. The server becomes unresponsive or severely degraded in performance.
The root cause lies in the design of Google V8's hash function used for form parameters. The function's implementation allows for predictable hash collisions. Attackers can craft a large number of parameters with specific values that map to the same hash value. When the application attempts to process these parameters, the hash table becomes severely degraded, leading to a significant increase in CPU usage as the engine struggles to resolve collisions. This is not a buffer overflow or memory corruption issue, but rather a algorithmic complexity problem, specifically an O(n^2) or worse performance characteristic when handling hash collisions. The lack of collision resistance in the hash function allows for the creation of a 'hash collision DoS' attack.