Recently, Apple patched a potentially serious vulnerability tracked as CVE-2025-24123. This flaw affects the way certain Apple operating systems parse files, and could lead to unexpected app crashes—think abrupt closures or loss of unsaved work. In this article, we break down what happened, why it matters, and—most importantly—how users and developers can protect themselves.

We'll also show a code snippet demonstrating how a malicious file could exploit the bug, share original references, and explain how Apple addressed the issue.

What is CVE-2025-24123?

CVE-2025-24123 is a vulnerability that stems from insufficient checks while parsing certain files on affected Apple platforms. If an attacker can trick you (or your app) into opening a malicious file, it could cause that app to crash without warning. In some edge cases (according to Apple), such crashes could potentially lead to more serious consequences like denial-of-service.

What Happens In Practice?

At its core, this vulnerability is an input validation issue. A specially crafted file with abnormal data (for example, an invalid header or malformed fields) could trick the app into an unexpected state, making it crash.

Proof-of-Concept Code Snippet

Let's look at a simplified example in Swift that simulates what might go wrong when parsing a file with expecting a certain format—but that format is violated.

Suppose a parser expects the first 4 bytes to be a "magic number" and the next 4 bytes to be an integer representing the section size. What if the file is too short, or the section size is huge?

import Foundation

func parseFile(_ data: Data) {
    // Check if data is long enough for header
    guard data.count >= 8 else {
        print("File too short!")
        return
    }
    // Extract "section size"
    let sectionSize = data.subdata(in: 4..<8).withUnsafeBytes { $.load(as: UInt32.self) }
    // Vulnerable: doesn't check if sectionSize is realistic
    let sectionEnd = 8 + Int(sectionSize)
    let sectionData = data.subdata(in: 8..<sectionEnd) // CRASH if sectionEnd > data.count!
    print("Section data read:", sectionData)
}

// The malicious file: only 12 bytes, but claims sectionSize is 10000
let maliciousFile = Data([xDE, xAD, xBE, xEF, x10, x27, x00, x00] + [UInt8](repeating: , count: 4))
// parseFile will try to read beyond the buffer
parseFile(maliciousFile)

Above: If sectionSize is big, but the file is small, this code will try to access memory beyond the end of the file buffer, causing a crash.

Note: Apple's proprietary code is closed, but this demonstrates the general principle.

- Apple Security Updates for CVE-2025-24123
- CVE Details: CVE-2025-24123

How Did Apple Fix It?

According to Apple, the issue was addressed with improved checks. That means their engineers added extra steps to confirm the file's validity before working with its data—which is exactly what robust code should do.

A fixed version might look like this

func parseFileSafely(_ data: Data) {
    guard data.count >= 8 else {
        print("File too short!")
        return
    }
    let sectionSize = data.subdata(in: 4..<8).withUnsafeBytes { $.load(as: UInt32.self) }
    let sectionEnd = 8 + Int(sectionSize)
    // Extra check:
    guard sectionEnd <= data.count else {
        print("Section size is invalid!")
        return
    }
    let sectionData = data.subdata(in: 8..<sectionEnd)
    print("Section data read:", sectionData)
}

Recommendations

- Update Now: If you are running any version prior to the above mentioned patched releases, update your devices ASAP.
- Be Careful With Untrusted Files: Don't open files from sources you can't trust, especially if you haven't updated yet.

Conclusion

CVE-2025-24123 is a classic file parsing bug that highlights the importance of input validation—especially in operating systems with millions of users. Apple’s quick response shows how seriously vendors take bugs that could harm stability or user data.

For more technical details, check the following sources

- Apple Security Update Notes
- CVE Database Entry

Stay safe—update your Apple devices regularly!

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Timeline

Published on: 01/27/2025 22:15:17 UTC
Last modified on: 03/03/2025 22:45:38 UTC