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

● CVE-2023-32558 · CVSS 7.5 · Hoch
Sicherheitsforschung · FlawOpen

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

Detaillierte technische Quellcode-Analyse und Härtungsmaßnahmen für vulnerabilidade: How accessing low-level C++ internal bindings via process.binding('fs') bypassed the experimental --permission --allow-fs-read flags.

💡 Einfache Erklärung (ELI5)

Anschauliche Analogie: 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.

Kernkonzepte & Begriffe

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.

Ursachenanalyse

Die Grundursache liegt in nicht validierten Grenzparametern in Open-Source-Systemen, die eine Zustandsdesynchronisation und die Umgehung von Sicherheitskontrollen ermöglichen.

Schritt-für-Schritt Angriffsablauf

Step 1

Angriffsphase: Start Sandboxed Node.js Process

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

Step 2

Angriffsphase: Access Internal Binding

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

Step 3

Angriffsphase: Bypass High-Level JS Checks

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

Step 4

Angriffsphase: Arbitrary System File Read

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

Quellcode: Verwundbar vs. Sicher

VERWUNDBARE IMPLEMENTIERUNG
// 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);
}
GEHÄRTETER SICHERHEITS-PATCH
// 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);
}

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