● CVE-2024-22019 / Sandbox Escape

CVE-2024-22019: Node.js Permission Model Filesystem Escape Teardown

How accessing low-level C++ internal bindings via process.binding('fs') bypassed the experimental --permission --allow-fs-read flags.

💡 Explication en Termes Simples (ELI5)

Imagine a high-security office building with security guards at the front doors checking badges. A worker who doesn't have a badge walks around back, opens the maintenance door marked 'Internal Staff Only', and walks straight into the vault. In Node.js, the developer guarded the public JavaScript functions, but forgot to lock the underlying C++ internal door.

Concepts Clés et Termes du Sous-système

Node.js Permission Model: The experimental `--permission` CLI flag restricting process capabilities like filesystem, child process, and worker access.
process.binding(): The legacy internal Node.js API that directly exposes native C++ bindings to JavaScript code.
Path Containment: Ensuring file operations remain strictly inside specified directory boundaries.
Defense-in-Depth: Enforcing security checks at the lowest possible layer (native C++ layer) rather than superficial JS wrappers.

Mécanique d'Exécution Étape par Étape

Step 1

1. Start Sandboxed Node.js Process

A developer runs untrusted code with node --permission --allow-fs-read=/tmp app.js.

Step 2

2. Access Internal Binding

The script invokes const binding = process.binding('fs');.

Step 3

3. Bypass High-Level JS Checks

The script calls binding.open('/etc/passwd') directly, bypassing fs.readFile() wrappers.

Step 4

4. Arbitrary System File Read

The native C++ binding executes without permission checks, leaking confidential server files.

Code Source : Faille Critique vs. Correctif Sécurisé

Fourni en code source de haut niveau lisible (sans assembleur brut ni diff binaire).

FAILLE NON CORRIGÉE

// VULNERABLE: src/node_file.cc before patch
static void Open(const FunctionCallbackInfo<Value>& args) {
    Environment* env = Environment::GetCurrent(args);
    
    // ROOT CAUSE:
    // Only verified permissions if called through JS 'fs' module wrappers!
    // Direct callers of process.binding('fs').open() evaded the check!
    const char* path = *Utf8Value(env->isolate(), args[0]);
    int fd = uv_fs_open(..., path, ...);
    args.GetReturnValue().Set(fd);
}

CORRECTIF RENFORCÉ

// SECURE: src/node_file.cc patch
static void Open(const FunctionCallbackInfo<Value>& args) {
    Environment* env = Environment::GetCurrent(args);
    
    const char* path = *Utf8Value(env->isolate(), args[0]);
    
    // 1. Enforce permission verification directly inside native C++ binding layer
    if (env->permission()->is_enabled()) {
        if (!env->permission()->is_granted(PermissionScope::kFileSystemRead, path)) {
            THROW_ERR_ACCESS_DENIED(env, "Access to path %s denied by Permission Model", path);
            return;
        }
    }
    
    int fd = uv_fs_open(..., path, ...);
    args.GetReturnValue().Set(fd);
}

Checklist d'Ingénierie et de Durcissement Système

Enforce security policy checks at the lowest possible native C++ layer, never solely in high-level JS wrappers.
Restrict access to `process.binding()` and internal Node.js modules from user-space code.
Combine Node.js permission model flags with OS-level sandboxing (Docker, seccomp, Linux namespaces).
Update Node.js runtimes to apply the latest security fixes to experimental runtime security features.

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