sentinel-modsec

Pure Rust ModSecurity implementation with full OWASP CRS compatibility.

A complete ModSecurity rule engine written in Rust with zero C/C++ dependencies. Load and execute OWASP Core Rule Set (CRS) rules for web application firewall (WAF) functionality in any Rust application.

Performance: 10-30x Faster than libmodsecurity

Features

• Full OWASP CRS Compatibility - Parse and execute 800+ CRS rules
• Pure Rust - No libmodsecurity, no C/C++ dependencies, no FFI
• SecLang Support - Load standard ModSecurity .conf rule files
• Built-in Detection - Native @detectSQLi and @detectXSS operators (pure Rust libinjection)
• All Operators - @rx, @pm, @pmFromFile, @contains, @streq, @ipMatch, and 30+ more
• All Transformations - t:lowercase, t:urlDecode, t:base64Decode, t:htmlEntityDecode, and 30+ more
• Thread-Safe - Send + Sync, safe for concurrent request processing
• Async-Ready - Works with tokio, async-std, or any async runtime
• Zero Unsafe - #![deny(unsafe_code)]

Quick Start

Add to your Cargo.toml:

[dependencies]
sentinel-modsec = "0.1"

Basic Usage

use sentinel_modsec::{ModSecurity, Rules, Transaction};

fn main() -> sentinel_modsec::Result<()> {
    // Create the ModSecurity engine
    let modsec = ModSecurity::new();

    // Load rules
    let mut rules = Rules::new();
    rules.add_plain("SecRuleEngine On")?;
    rules.add_plain(r#"
        SecRule REQUEST_URI "@contains /admin" \
            "id:1,phase:1,deny,status:403,msg:'Admin access blocked'"
    "#)?;

    // Compile rules (do this once, reuse for all requests)
    let ruleset = rules.compile()?;

    // Process a request
    let mut tx = modsec.transaction(&ruleset);
    tx.process_uri("/admin/dashboard", "GET", "HTTP/1.1")?;
    tx.add_request_header("Host", "example.com")?;
    tx.add_request_header("User-Agent", "Mozilla/5.0")?;
    tx.process_request_headers()?;

    // Check for intervention (block/redirect/etc)
    if let Some(intervention) = tx.intervention() {
        println!("Blocked: status={}, rule={:?}",
            intervention.status,
            intervention.rule_id);
    }

    Ok(())
}

Loading OWASP CRS Rules

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();

    // Load CRS setup
    rules.add_file("/etc/modsecurity/crs/crs-setup.conf")?;

    // Load all CRS rules (glob patterns supported)
    rules.add_file("/etc/modsecurity/crs/rules/*.conf")?;

    let ruleset = rules.compile()?;

    println!("Loaded {} rules", ruleset.rule_count());

    Ok(())
}

SQL Injection Detection

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();
    rules.add_plain(r#"
        SecRuleEngine On
        SecRule ARGS "@detectSQLi" \
            "id:942100,phase:2,deny,status:403,msg:'SQL Injection detected'"
    "#)?;

    let ruleset = rules.compile()?;
    let mut tx = modsec.transaction(&ruleset);

    // Simulate a request with SQLi payload
    tx.process_uri("/search?q=' OR 1=1--", "GET", "HTTP/1.1")?;
    tx.process_request_headers()?;

    assert!(tx.has_intervention());
    println!("SQLi attack blocked!");

    Ok(())
}

XSS Detection

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();
    rules.add_plain(r#"
        SecRuleEngine On
        SecRule ARGS "@detectXSS" \
            "id:941100,phase:2,deny,status:403,msg:'XSS detected'"
    "#)?;

    let ruleset = rules.compile()?;
    let mut tx = modsec.transaction(&ruleset);

    tx.process_uri("/comment?text=<script>alert(1)</script>", "GET", "HTTP/1.1")?;
    tx.process_request_headers()?;

    assert!(tx.has_intervention());
    println!("XSS attack blocked!");

    Ok(())
}

Request Body Inspection

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();
    rules.add_plain(r#"
        SecRuleEngine On
        SecRequestBodyAccess On
        SecRule REQUEST_BODY "@detectSQLi" \
            "id:942110,phase:2,deny,status:403,msg:'SQLi in body'"
    "#)?;

    let ruleset = rules.compile()?;
    let mut tx = modsec.transaction(&ruleset);

    tx.process_uri("/api/login", "POST", "HTTP/1.1")?;
    tx.add_request_header("Content-Type", "application/x-www-form-urlencoded")?;
    tx.process_request_headers()?;

    // Add request body
    tx.append_request_body(b"username=admin&password=' OR 1=1--")?;
    tx.process_request_body()?;

    assert!(tx.has_intervention());

    Ok(())
}

Detection-Only Mode

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();
    rules.add_plain(r#"
        SecRuleEngine DetectionOnly
        SecRule REQUEST_URI "@contains /admin" "id:1,phase:1,deny"
    "#)?;

    let ruleset = rules.compile()?;
    let mut tx = modsec.transaction(&ruleset);

    tx.process_uri("/admin", "GET", "HTTP/1.1")?;
    tx.process_request_headers()?;

    // Rule matched but no intervention (detection only)
    assert!(!tx.has_intervention());
    assert!(tx.matched_rules().contains(&"1".to_string()));

    println!("Detected but not blocked: {:?}", tx.matched_rules());

    Ok(())
}

Anomaly Scoring

use sentinel_modsec::{ModSecurity, Rules};

fn main() -> sentinel_modsec::Result<()> {
    let modsec = ModSecurity::new();

    let mut rules = Rules::new();
    rules.add_plain(r#"
        SecRuleEngine On

        # Increment score for suspicious patterns
        SecRule REQUEST_URI "@contains /admin" \
            "id:1,phase:1,pass,setvar:'TX.anomaly_score=+5'"
        SecRule REQUEST_HEADERS:User-Agent "@contains sqlmap" \
            "id:2,phase:1,pass,setvar:'TX.anomaly_score=+10'"

        # Block if score exceeds threshold
        SecRule TX:anomaly_score "@ge 10" \
            "id:100,phase:1,deny,status:403,msg:'Anomaly score exceeded'"
    "#)?;

    let ruleset = rules.compile()?;
    let mut tx = modsec.transaction(&ruleset);

    tx.process_uri("/admin", "GET", "HTTP/1.1")?;
    tx.add_request_header("User-Agent", "sqlmap/1.0")?;
    tx.process_request_headers()?;

    println!("Anomaly score: {}", tx.anomaly_score());
    assert!(tx.has_intervention());

    Ok(())
}

Framework Integration

Axum

use axum::{
    body::Body,
    extract::State,
    http::{Request, StatusCode},
    middleware::{self, Next},
    response::Response,
    routing::get,
    Router,
};
use sentinel_modsec::{ModSecurity, CompiledRuleset};
use std::sync::Arc;

async fn waf_middleware(
    State(ruleset): State<Arc<CompiledRuleset>>,
    request: Request<Body>,
    next: Next,
) -> Result<Response, StatusCode> {
    let modsec = ModSecurity::new();
    let mut tx = modsec.transaction(&ruleset);

    // Process request
    tx.process_uri(
        request.uri().path_and_query().map(|pq| pq.as_str()).unwrap_or("/"),
        request.method().as_str(),
        "HTTP/1.1",
    ).map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    for (name, value) in request.headers() {
        if let Ok(v) = value.to_str() {
            let _ = tx.add_request_header(name.as_str(), v);
        }
    }

    tx.process_request_headers()
        .map_err(|_| StatusCode::INTERNAL_SERVER_ERROR)?;

    // Check for intervention
    if let Some(intervention) = tx.intervention() {
        return Err(StatusCode::from_u16(intervention.status).unwrap_or(StatusCode::FORBIDDEN));
    }

    Ok(next.run(request).await)
}

#[tokio::main]
async fn main() {
    let mut rules = sentinel_modsec::Rules::new();
    rules.add_file("/etc/modsecurity/crs/rules/*.conf").unwrap();
    let ruleset = Arc::new(rules.compile().unwrap());

    let app = Router::new()
        .route("/", get(|| async { "Hello, World!" }))
        .layer(middleware::from_fn_with_state(ruleset.clone(), waf_middleware))
        .with_state(ruleset);

    let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
    axum::serve(listener, app).await.unwrap();
}

Actix-web

use actix_web::{web, App, HttpServer, HttpRequest, HttpResponse, middleware};
use sentinel_modsec::{ModSecurity, CompiledRuleset};
use std::sync::Arc;

async fn waf_check(
    req: HttpRequest,
    ruleset: web::Data<Arc<CompiledRuleset>>,
) -> Option<HttpResponse> {
    let modsec = ModSecurity::new();
    let mut tx = modsec.transaction(&ruleset);

    tx.process_uri(req.uri().path_and_query().map(|pq| pq.as_str()).unwrap_or("/"),
                   req.method().as_str(),
                   "HTTP/1.1").ok()?;

    for (name, value) in req.headers() {
        if let Ok(v) = value.to_str() {
            let _ = tx.add_request_header(name.as_str(), v);
        }
    }

    tx.process_request_headers().ok()?;

    tx.intervention().map(|i| {
        HttpResponse::build(actix_web::http::StatusCode::from_u16(i.status).unwrap())
            .body(format!("Blocked by rule: {:?}", i.rule_id))
    })
}

Supported SecLang Directives

Directives

Operators

Transformations

Actions

Why Pure Rust?

1. Performance - 10-30x faster than C++ libmodsecurity
2. Safety - Memory safety guaranteed, no buffer overflows
3. Portability - Runs anywhere Rust compiles (including WASM)
4. Simplicity - cargo add sentinel-modsec, no system dependencies
5. Auditability - Single-language codebase, easier security review

Technical Optimizations

• PHF (Perfect Hash Functions) - O(1) operator/variable lookup
• Lazy Regex Compilation - Defer compilation to first use
• Aho-Corasick - O(n) multi-pattern matching for @pm
• RegexSet - Single-pass multi-regex evaluation for XSS detection
• Zero-Copy Parsing - Cow<str> avoids allocations when possible
• No FFI Overhead - Pure Rust, no cross-language calls

OWASP CRS Setup

# Download OWASP Core Rule Set
git clone https://github.com/coreruleset/coreruleset /etc/modsecurity/crs
cp /etc/modsecurity/crs/crs-setup.conf.example /etc/modsecurity/crs/crs-setup.conf

# Use in your application
rules.add_file("/etc/modsecurity/crs/crs-setup.conf")?;
rules.add_file("/etc/modsecurity/crs/rules/*.conf")?;

Comparison

License

Apache-2.0

Contributing

Contributions welcome! Please read CONTRIBUTING.md for guidelines.

Related Projects

• Sentinel - Extensible reverse proxy using this engine
• OWASP CRS - Core Rule Set for ModSecurity
• libmodsecurity - Original C++ implementation