flawopen.com/Teardowns/cve-2023-32558-nodejs-permission-model-fs-escape

● CVE-2023-32558 · CVSS 7.5 · Alta
Pesquisa · FlawOpen

CVE-2023-32558: Node.js Permission Model Filesystem Escape Teardown

Análise técnica detalhada e engenharia de mitigação do patch para vulnerabilidade: How accessing low-level C++ internal bindings via process.binding('fs') bypassed the experimental --permission --allow-fs-read flags.

💡 Explicação em Linguagem Simples (ELI5)

Analogia explicativa: 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.

Conceitos Centrais e Termos

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.

Análise de Causa Raiz

A causa raiz decorre de parâmetros de limite não validados em sistemas de código aberto, permitindo a dessincronização de estado e a evasão dos controles de segurança.

Fluxo de Ataque Passo a Paso

Step 1

Fase de ataque: Start Sandboxed Node.js Process

Mecanismo de exploração técnica: A developer runs untrusted code with node --permission --allow-fs-read=/tmp app.js.

Step 2

Fase de ataque: Access Internal Binding

Mecanismo de exploração técnica: The script invokes const binding = process.binding('fs');.

Step 3

Fase de ataque: Bypass High-Level JS Checks

Mecanismo de exploração técnica: The script calls binding.open('/etc/passwd') directly, bypassing fs.readFile() wrappers.

Step 4

Fase de ataque: Arbitrary System File Read

Mecanismo de exploração técnica: The native C++ binding executes without permission checks, leaking confidential server files.

Código-Fonte: Vulnerável vs. Seguro

IMPLEMENTAÇÃO VULNERÁVEL
// 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);
}
PATCH SEGURO E ROBUSTO
// 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);
}

Lista de Verificação de Segurança para Engenharia

Fontes