Fix Unrestricted Resource Consumption in Actix Web

Actix Web is built for speed, but speed is useless if a single malicious request can trigger an Out of Memory (OOM) event. Unrestricted resource consumption in Actix usually stems from unbounded request bodies or excessive memory allocation during payload extraction. If you don't explicitly cap your extractors, you're leaving the door open for DoS attacks via memory exhaustion.

The Vulnerable Pattern

use actix_web::{post, web, App, HttpResponse, HttpServer};
#[post(“/data”)]
async fn leak_memory(payload: String) -> HttpResponse {
// VULNERABLE: String extractor uses default limits which might be too high,
// or worse, if custom limits are removed, it can consume massive RAM.
HttpResponse::Ok().body(format!(“Processed {} bytes”, payload.len()))
}
#[actix_web::main]
async fn main() -> std::io::Result<()> {
HttpServer::new(|| {
App::new().service(leak_memory)
})
.bind(“127.0.0.1:8080”)?
.run()
.await
}

The Secure Implementation

The exploit vector involves an attacker sending a 'Content-Length' header with a large value followed by a massive stream of bytes. In the vulnerable version, the server attempts to buffer this into memory. The fix involves using 'app_data' to inject configuration objects (JsonConfig, FormConfig, PayloadConfig) that strictly enforce maximum byte sizes. When a request exceeds these limits, Actix immediately returns a 413 Payload Too Large response, terminating the stream and protecting the heap from exhaustion.

use actix_web::{post, web, App, HttpResponse, HttpServer};
#[post(“/data”)]
async fn secure_handler(payload: String) -> HttpResponse {
HttpResponse::Ok().finish()
}
#[actix_web::main]
async fn main() -> std::io::Result<()> {
HttpServer::new(|| {
App::new()
// SECURE: Explicitly limit JSON payloads to 4KB
.app_data(web::JsonConfig::default().limit(4096))
// SECURE: Explicitly limit Form payloads to 4KB
.app_data(web::FormConfig::default().limit(4096))
// SECURE: Global payload limit for raw bytes/strings (e.g., 8KB)
.app_data(web::PayloadConfig::new(8192))
.service(secure_handler)
})
.bind(“127.0.0.1:8080”)?
.run()
.await
}

Protect your Actix Web API

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The Vulnerable Pattern

The Secure Implementation

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Verified by Ghost Labs Security Team