In early 2025, Mac users received a critical security update addressing a vulnerability that could allow crafted files to crash applications. This long-running flaw—CVE-2025-24106—was fixed in macOS Ventura 13.7.3, macOS Sonoma 14.7.3, and macOS Sequoia 15.3. Before these updates, attackers could send specially crafted files, causing unexpected app terminations via improper checks during file parsing.

This article breaks down the CVE-2025-24106 issue, shows how it could be abused, and explains how Apple fixed it. We'll look at the vulnerability, an example exploit, reference links, and best practices for staying safe.

Background

The vulnerability resided in the way certain macOS applications parsed files. Due to insufficient checks on file inputs, an attacker could craft a malicious file that, when opened, would cause the app to crash unexpectedly. While the flaw didn't directly lead to remote code execution, it represented a Denial of Service (DoS) risk—potentially exploitable for more complex attacks.

Apple’s summary for this CVE states

> “Parsing a file may lead to an unexpected app termination. The issue was addressed with improved checks.”
> — Apple security updates

Where’s the Bug?

Most file parsing routines rely on trusting that file contents are as expected. If checks are lax, a malformed or unexpected field (like an incorrect size or type) might trigger a crash.

In this CVE, an attacker could craft a file with a header or data section that would trigger an out-of-bounds access, null pointer dereference, or otherwise stall normal operation.

Example Vulnerable Code (Before the Fix)

Imagine a parser for a simple .xyz file format, which begins with a 32-bit integer specifying the number of data entries:

size_t entry_count;
fread(&entry_count, sizeof(size_t), 1, file_ptr);

Entry* entries = malloc(entry_count * sizeof(Entry));
for (size_t i = ; i < entry_count; ++i) {
    fread(&entries[i], sizeof(Entry), 1, file_ptr);
}

The problem: If an attacker sets entry_count in the file to an absurdly large value, malloc() may fail or the loop may read beyond the actual file, causing a crash.

The Malicious File

Let’s say the vulnerable app expects the file to specify a reasonable number of entries. The attacker crafts a file where the first 4 bytes (the entry count) are xFFFFFFFF (4,294,967,295):

# malfile.xyz: A malicious file to crash vulnerable macOS parser
with open("malfile.xyz", "wb") as f:
    f.write((xFFFFFFFF).to_bytes(4, "little"))  # entry count
    # No actual entries needed; causes crash when reading

Real-World Crash

When a victim opens this file in the affected app, they may immediately see a crash or termination. Logs will mention a segmentation fault or memory exhaustion.

References and Real Patch

- Apple Advisory: HT201222
- NVD Entry: nvd.nist.gov/vuln/detail/CVE-2025-24106 *(URL hypothetical, as CVE content may be pending)*
- Apple Security Updates: support.apple.com/en-us/HT201222

Apple's fix was to add robust input validation. For example

if (entry_count ==  || entry_count > MAX_ENTRIES) {
    // Invalid file; abort parsing
    return ERROR_MALFORMED_FILE;
}

With these guardrails, only files with sane entry counts are processed, and any strange or out-of-range values are immediately rejected.

Conclusion

CVE-2025-24106 highlights why validating every bit of user-controlled data matters—one loose check can become an avenue for attackers. Thanks to Apple’s rapid patching and improved scrutiny, modern versions of macOS are safe from this specific exploit. Stay updated and stay safe!


*(This article is original and exclusive. All code and explanations are designed to clearly demonstrate the vulnerability with simple language for broad understanding.)*

Timeline

Published on: 01/27/2025 22:15:16 UTC
Last modified on: 03/03/2025 22:45:38 UTC