5.2.2 Ensure the maximum request body size is set correctly

Information

The client_max_body_size directive defines the maximum permissible size for a client request body, as indicated by the Content-Length header. If a request exceeds this size, NGINX will immediately reject it with a 413 Request Entity Too Large error, preventing the oversized request from being processed further or passed to a backend application.

Limiting the request body size is a crucial defense against resource exhaustion DoS attacks and prevents oversized, potentially malicious payloads from reaching application backends. By setting a logical default limit and only increasing it for specific application endpoints that require it (e.g., file uploads), the principle of least functionality is enforced, significantly reducing the attack surface.

NOTE: Nessus has provided the target output to assist in reviewing the benchmark to ensure target compliance.

Solution

Define a restrictive global limit in the http block. For specific application endpoints that need to accept larger request bodies, override this directive within the corresponding location block.

Example Configuration:

http {

# Set a restrictive global default of 2 Megabytes. This prevents unexpected large requests on most endpoints.
client_max_body_size 2M;

server {
# ...

# This location handles API requests with potentially large JSON payloads.
location /api/v1/data {
client_max_body_size 10M; # Allow up to 10MB
# ...
}

# This location is for large file uploads.
location /uploads {
client_max_body_size 50M; # Allow up to 50MB
# ...
}
}
}

Impact:

Setting this value too low is a common cause of application failure. Legitimate user actions, such as uploading files or submitting large forms, will be blocked with a 413 error if they exceed the configured limit. It is essential that this value is determined based on application requirements and not set to an arbitrary low number.

See Also

https://workbench.cisecurity.org/benchmarks/18528

Item Details

Category: SYSTEM AND SERVICES ACQUISITION

References: 800-53|SA-3, CSCv7|18.1

Plugin: Unix

Control ID: a0cba7f3f110249cccbff339fbba37e03c664841a3a29a61fbb7d9d027d415ca