In late 2022, Apple patched a significant security issue, now tracked as CVE-2022-42810, which affected how several Apple operating systems handled Universal Scene Description (USD) files. This post will break down the vulnerability, show you how attackers could exploit it, and explain what Apple did to fix it, with code snippets and references for further learning.

Summary:
*“Processing a maliciously crafted USD file may disclose memory contents.”*
This kind of bug can let attackers read private memory, leaking credentials, sensitive information, or even program logic.

What is a USD File?

USD (Universal Scene Description) is a 3D scene file format used in animation and AR/VR workflows. Apple’s operating systems natively support USD for content creation and viewing.

The Weakness: Poor Memory Handling

The bug was in how Apple’s parser handled USD files. If an attacker creates a malformed USD file, opening it could cause the parser to inadvertently leak chunks of device memory. That memory could hold sensitive information like passwords or personal data.

The Apple security advisory describes

> “Processing a maliciously crafted USD file may disclose memory contents. This issue was addressed with improved memory handling.”

Example Exploitation Scenario

Suppose an attacker sends a crafted USD file to a victim, urging them to open it on a vulnerable device (maybe as an email attachment). If the victim opens it, hidden malicious content in the file extracts parts of RAM, sending private data back to the attacker.

Because Apple controls the parsing code and hasn’t fully disclosed the bug’s details, we can only reason about what likely went wrong.

Likely Attack: Out-of-bounds Read

Most bugs like this come from *out-of-bounds reads* or *uninitialized memory use*. For illustration, here’s a simple C++ example of an unsafe deserialization routine that might cause such info leaks:

#include <iostream>
#include <fstream>
#include <cstring>

void loadUSD(const char* filename) {
    char buffer[1024];
    std::ifstream file(filename);

    if (!file) {
        std::cerr << "File can't be opened!\n";
        return;
    }

    // Imagine the USD file is larger than the buffer
    file.read(buffer, 2048);

    // Now behave as if buffer has valid data
    if (strstr(buffer, "malicious_payload")) {
        // Do something dangerous
        printf("Sensitive info: %s\n", buffer + 150); // Out of bounds!
    }

    file.close();
}

Here, reading more data than the buffer’s size, then operating on it, could leak memory. If Apple had a similar out-of-bounds read or failed to initialize memory before returning part of a USD structure, an attacker could embed a marker (“malicious_payload”) that triggers memory disclosure.

The Real-World Impact

This bug lets attackers steal parts of your device’s memory just by opening a crafted USD file. Private data, like texts, passwords, or image contents, could be exposed.

If you’re on any Apple device released before the fixed versions, someone could target you via email, web downloads, or AirDrop.

Mitigation

Apple issued patches fixing the bug by “improved memory handling.” In practice, they probably added extra checks like this:

// Instead of risking uninitialized memory:
char buffer[1024] = {}; // Ensures any unused space is zeroed out

if (bytesRead < sizeof(buffer)) {
    memset(buffer + bytesRead, , sizeof(buffer) - bytesRead);
}

Or they might have added stricter file format validation to block malformed files earlier.

Exploit Steps (Theoretically)

1. Create Malicious USD File: Craft a USD file with bad structure or special payloads at certain offsets.

Victim Opens File: Device's USD parser reads the file.

4. Leak Occurs: Parser copies internal memory into an exposed part of the file processing, sending or displaying it.

Suppose you’re reverse engineering the parser (for research)

# Pseudo code: Creating USD file with overlong field
with open("crafted.usd", "wb") as f:
    f.write(b"#usda 1.\n")  # header
    f.write(b"def Xform \"scene\" {\n")
    f.write(b"  customData = \"")
    f.write(b"A" * 300)    # Overlong field to trigger leak
    f.write(b"\"\n}\n")

When opened on a vulnerable device, any unexpected or extra “garbage” in the output could hint at memory disclosure.

- Apple Security Updates - CVE-2022-42810
- Mitre CVE Entry
- Universal Scene Description Format
- macOS 13 Ventura Security Content

Conclusion

If you haven’t updated your Apple devices to the fixed versions, you risk memory leaks just by opening a 3D USD file. Apply the latest system updates right away.

Problems like this show how subtle bugs in file parsing can have deep security impacts. Always patch early, and be careful with files from unknown sources — even cool-looking 3D scenes!

Timeline

Published on: 11/01/2022 20:15:00 UTC
Last modified on: 11/03/2022 03:54:00 UTC