Source: cve@mitre.org
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.
Google V8, the JavaScript engine, is vulnerable to a denial-of-service (DoS) attack due to predictable hash collisions in its form parameter handling. Attackers can exploit this flaw by sending a large number of crafted parameters, leading to excessive CPU consumption and potentially rendering services unresponsive.
Step 1: Payload Preparation: The attacker crafts a set of form parameters designed to collide within the V8 hash function. This involves generating parameter keys that, when hashed, produce the same hash value.
Step 2: Payload Delivery: The attacker sends a request (e.g., HTTP POST) containing the crafted parameters to a vulnerable application using V8.
Step 3: Hash Calculation: The V8 engine processes the form parameters and calculates hash values for each parameter key.
Step 4: Collision Triggering: Due to the crafted parameters, multiple keys hash to the same value, resulting in hash collisions.
Step 5: CPU Exhaustion: The engine spends significant CPU cycles resolving these collisions, leading to a denial-of-service condition as the server becomes overloaded.
Step 6: Service Degradation: Legitimate requests are delayed or dropped, rendering the application or service unavailable.
The vulnerability stems from the V8 engine's implementation of hash functions for form parameters. The hash function used is susceptible to hash collisions, where different inputs produce the same hash value. Attackers can craft malicious input designed to trigger these collisions repeatedly. When a large number of collisions occur, the engine spends an excessive amount of time resolving these collisions, leading to high CPU usage. The root cause is the lack of robust collision resistance in the hash function, allowing attackers to control the hash values and force collisions. This is a weakness in the algorithm's design, not a memory corruption issue like a buffer overflow or a race condition.
While no specific APTs are directly linked to CVE-2011-5037, the underlying technique of hash collision attacks is used by various threat actors for denial-of-service. This vulnerability is not listed in the CISA KEV database, but the general class of DoS attacks is a constant threat vector.
High CPU utilization on the server, particularly during periods of increased traffic.
Unusually slow response times from the affected application.
Network traffic analysis showing a large number of requests with crafted parameters.
Application logs showing excessive processing time for specific requests.
Monitoring for requests with a large number of parameters, especially if the parameter keys appear to be crafted or repetitive.
Upgrade or patch the affected JavaScript engine (V8) if possible. However, this is often not directly possible as it is embedded in other products.
Implement rate limiting to restrict the number of requests from a single source within a specific time frame.
Implement input validation to limit the number and size of form parameters.
Use a more robust hash function or a hash function with collision resistance, if possible.
Consider using a different data structure (e.g., a tree) for storing form parameters if hash collisions are a persistent problem.
Implement a WAF (Web Application Firewall) with rules to detect and block requests containing a large number of parameters or suspicious parameter keys.
Monitor server resource usage (CPU, memory) and set alerts for unusual spikes.