Log Injection in Actix with Api Keys

Log injection occurs when untrusted input is written directly into application logs without validation or encoding. In Actix-based Rust services that rely on API keys for authentication, this becomes especially relevant because API keys are often logged for request tracing, auditing, or debugging. If an API key value or a key-derived identifier (such as a key ID or associated username) is reflected in log output without sanitization, an attacker can inject newline characters or structured log tokens that alter the log’s format or inject additional entries.

Consider an Actix handler that authenticates a request by checking an API key query parameter or header and then logs the key or its metadata:

use actix_web::{web, App, HttpResponse, HttpServer, Responder};
use log::info;

async fn handle_request(api_key: web::Query<ApiKey>) -> impl Responder {
    // Log the incoming API key for debugging
    info!("Request with API key: {}", api_key.key);
    HttpResponse::Ok().finish()
}

#[derive(serde::Deserialize)]
struct ApiKey {
    key: String,
}

If api_key.key contains newline characters (e.g., abc123\n%20injected:true), the log line can break into multiple entries or append structured data that log parsers interpret as separate events. This can obscure the origin of log lines, complicate correlation with request IDs, and in systems that treat structured fields (like key-value pairs) as metadata, may lead to log injection that supports log forging or log poisoning attacks.

Because API keys are high-value secrets, exposing them in logs—even via injection—can amplify risk. An attacker who can inject content might also attempt to exfiltrate other keys or metadata through crafted payloads. In an Actix service, the vulnerability is not in Actix itself but in how the application handles and logs the API key values. Without input validation, sanitization, or structured logging practices, log injection in this context can degrade auditability and assist in further attacks such as log-based pivoting or social engineering.

Remediation focuses on preventing untrusted API key values from corrupting log structure and ensuring that logs remain parseable and auditable. The safest approach is to avoid logging raw API key values entirely. If logging is required for operational reasons, log only a non-sensitive identifier (e.g., key ID or a hash) and sanitize any user-controlled data before it reaches the logging layer.

Example: Log a key identifier instead of the full key, and sanitize inputs that may be used in structured logging contexts:

use actix_web::{web, App, HttpResponse, HttpServer, Responder};
use log::info;
use sanitize::Sanitize; // hypothetical crate for illustration; implement escaping as needed

async fn handle_request(api_key: web::Query<ApiKey>) -> impl Responder {
    // Derive a safe representation: key ID or hash, never the full key
    let key_id = compute_key_id(&api_key.key);
    // Sanitize any user-controlled metadata if used in structured logs
    let source_ip = sanitize_input(&api_key.source_ip);
    info!(key_id = %key_id, source_ip = %source_ip, "authenticated request");
    HttpResponse::Ok().finish()
}

fn compute_key_id(key: &str) -> String {
    // Example: first 8 chars of SHA256 hash; do not log the raw key
    use sha2::{Sha256, Digest};
    let mut hasher = Sha256::new();
    hasher.update(key);
    let hash = hasher.finalize();
    format!("{:x}", &hash[..8])
}

fn sanitize_input(value: &str) -> String {
    value.replace(['\n', '\r'], "_")
}

#[derive(serde::Deserialize)]
struct ApiKey {
    key: String,
    #[serde(rename = "sourceIp")]
    source_ip: String,
}

Additional measures include using structured logging frameworks that enforce strict schemas and escaping, ensuring that newline characters are either rejected or encoded so they do not break log lines. In an Actix pipeline, you can also centralize authentication and logging middleware to enforce these rules consistently across endpoints. These practices align with findings reported by scanners such as middleBrick, which highlight log injection risks in API key handling and provide prioritized remediation steps tied to frameworks like OWASP API Top 10 and compliance mappings.

For continuous validation, teams can integrate scans using the middleBrick CLI (middlebrick scan <url>) or GitHub Action to fail builds when insecure logging patterns are detected in reachable API endpoints. The dashboard can track these findings over time, and the Pro plan enables scheduled monitoring and alerts to prevent regression as code evolves.