Understanding CVE-2025-43300: An Out-of-Bounds Write Vulnerability in Apple macOS and iOS

Have you ever wondered what happens when a simple image file turns into a potential security risk? That’s exactly the case with CVE-2025-43300, a vulnerability affecting several versions of Apple’s operating systems. In this article, we’ll break it down step by step, explaining the issue in clear terms so you can grasp why it matters and what it involves. I’ll walk you through the details as if we’re discussing it over coffee, answering questions you might have along the way.

First off, let’s talk about what this vulnerability is. CVE-2025-43300 refers to an out-of-bounds write problem in specific Apple macOS and iOS versions. This means that when the system processes certain maliciously crafted image files, it doesn’t check the boundaries properly, leading to writing data outside the intended memory area. As a result, attackers could remotely cause memory corruption. The exploit requires a specially designed malicious image file to trigger it.

Why is this important for you? If you’re using devices like Macs, iPhones, or iPads running the affected software, understanding this can help you stay informed about potential risks. We’ll cover the affected versions, the severity, and even how proof-of-concept materials are handled in related tools like Nuclei templates.

What Is an Out-of-Bounds Write Vulnerability?

Imagine you’re writing a letter on a piece of paper, but instead of staying within the lines, your pen slips off the page and marks the table underneath. That’s similar to an out-of-bounds write in computing. In technical terms, it’s when a program tries to write data to a memory location that’s outside the allocated buffer or array. This happens due to improper bounds checking, where the software doesn’t verify if the operation stays within safe limits.

In the context of CVE-2025-43300, this occurs specifically when processing image files. If an attacker sends or tricks you into opening a malicious image, the system’s image processing code might write data beyond its intended memory space. This can lead to memory corruption, which is like scrambling important data in your computer’s memory. Memory corruption could potentially allow further exploitation, though the description focuses on the remote causation of this issue via the crafted file.

You might ask, “How does this differ from other vulnerabilities?” Well, out-of-bounds writes are a type of buffer overflow, but specifically for writing operations. They’re dangerous because they can overwrite critical data structures, potentially leading to crashes or more severe security breaches.

Which Apple Operating Systems Are Affected by CVE-2025-43300?

Let’s list out the exact versions mentioned. This vulnerability impacts:

• macOS Sonoma 14.7.8
• macOS Ventura 13.7.8
• iPadOS 17.7.10
• macOS Sequoia 15.6.1
• iOS 18.6.2
• iPadOS 18.6.2

If you’re running any of these, the issue stems from how these systems handle image processing. The problem is triggered remotely, but it requires interaction with a malicious image file. For example, opening such a file in an app that processes images could activate the vulnerability.

To make it easier to visualize, here’s a table summarizing the affected systems:

This table helps if you’re checking your device’s settings to see if it matches any of these.

How Does the Exploitation Work?

You might be thinking, “How exactly can an attacker use this?” The key is in crafting a malicious image file. This file is designed to exploit the improper bounds checking during image processing. When the system tries to read or render the image, it performs an out-of-bounds write, corrupting memory remotely.

It’s labeled as having a “High” severity, which indicates it’s a significant issue that could have serious implications if exploited. Also, it’s marked as KEV: True, meaning it’s known to be exploited in the wild or has been added to a catalog of known exploited vulnerabilities.

For those interested in testing or verifying, there’s a proof-of-concept (POC) available at https://github.com/h4xnz/CVE-2025-43300. This POC demonstrates how the vulnerability can be triggered using the crafted image file.

What about searching for vulnerable systems? The Shodan Query is listed as “NA,” which means there’s no specific Shodan query provided for identifying these vulnerabilities externally.

Contributing to Vulnerability Detection with Nuclei Templates

Now, let’s shift to how this ties into tools like Nuclei, which is a vulnerability scanner. The information comes from a GitHub issue on projectdiscovery/nuclei-templates, specifically issue #12953, published on August 22, 2025.

If you’re a developer or security researcher, you might want to contribute a template for detecting CVE-2025-43300 in Nuclei. The acceptance criteria are straightforward but strict:

• The template must include a complete POC.
• It should not rely solely on version-based detection; it needs to actively check for the vulnerability.
• Contributors need to provide debug data (using the -debug flag) with the template to aid validation.
• Alternatively, share a vulnerable environment, like a Docker file, for testing.

Rewards are part of the Nuclei Templates Community Rewards Program, but they’re only given once the template is fully validated by the team. Incomplete or invalid templates won’t be accepted.

There are also guidelines on what to avoid:

• Don’t create templates for CVEs that can be detected using HTTP, TCP, or JavaScript, as these are blocked by default and won’t yield results.
• Prioritize templates using other protocols, unless exceptions apply.

For more details on the program, check the FAQ at https://github.com/projectdiscovery/nuclei-templates/blob/main/Community-Rewards-FAQ.md.

If you’re new to this, contributing involves these steps:

1. Review the vulnerability details, including the POC.
2. Develop a Nuclei template that incorporates the complete POC and tests for the out-of-bounds write issue.
3. Run it with -debug to capture data.
4. Submit it via the GitHub issue or appropriate channel, ensuring it meets all criteria.

This process ensures high-quality templates that help in scanning for such vulnerabilities effectively.

Common Questions About CVE-2025-43300

To make this more conversational, let’s address some questions you might have. I’ll predict based on typical curiosities around vulnerabilities like this and answer them directly.

What causes the out-of-bounds write in CVE-2025-43300?

The root cause is improper bounds checking when processing malicious image files. Without proper checks, the system writes data outside the allocated memory, leading to corruption.

Is CVE-2025-43300 being actively exploited?

Yes, it’s marked as KEV: True, indicating it’s in the Known Exploited Vulnerabilities catalog.

How can I protect my Apple device from this vulnerability?

While the document doesn’t specify patches, being aware means watching for updates from Apple that address out-of-bounds write issues in image processing. Avoid opening suspicious image files from unknown sources.

What is a malicious image file in this context?

It’s a specially crafted file designed to trigger the vulnerability during processing, exploiting the lack of bounds checking.

Why is the severity rated as High?

Because it allows remote memory corruption, which could lead to further security risks if chained with other exploits.

Can I use Shodan to find devices vulnerable to CVE-2025-43300?

No, the Shodan Query is NA, so no specific query is provided.

How do I access the POC for CVE-2025-43300?

Visit https://github.com/h4xnz/CVE-2025-43300 for the proof-of-concept materials.

What are the exact affected versions again?

As listed earlier: macOS Sonoma 14.7.8, macOS Ventura 13.7.8, iPadOS 17.7.10, macOS Sequoia 15.6.1, iOS 18.6.2, and iPadOS 18.6.2.

Is this vulnerability remote or local?

It’s remote in the sense that an attacker can cause it by providing a malicious image file, but it requires the user to process that file.

How does memory corruption happen here?

Through the out-of-bounds write, which overwrites unintended memory areas, potentially destabilizing the system.

How to Contribute a Nuclei Template for CVE-2025-43300

If you’re interested in helping the community by creating a detection template, here’s a step-by-step guide based on the provided criteria.

Step 1: Understand the Requirements

Ensure your template includes a full POC and avoids version-only detection. It must actively exploit or detect the out-of-bounds write via the malicious image processing.

Step 2: Develop the Template

Use Nuclei’s YAML format. Incorporate the POC from https://github.com/h4xnz/CVE-2025-43300. Focus on protocols other than HTTP, TCP, or JavaScript to avoid blocking.

Step 3: Test with Debug Data

Run your template with the -debug flag to generate logs. This data is crucial for the triage team to validate.

Step 4: Provide a Vulnerable Environment (Optional but Helpful)

If possible, create a Docker file simulating the affected Apple environments for testing.

Step 5: Submit and Await Validation

Post your template in the relevant GitHub issue (#12953 on projectdiscovery/nuclei-templates). Rewards come only after full validation.

Potential Challenges and Tips

• Challenge: Ensuring the template doesn’t rely on blocked protocols.

  • Tip: Explore image processing workflows that use alternative methods.
• Challenge: Validating without a real device.

  • Tip: Use emulators or the provided vulnerable setup if available.

By following these steps, you contribute to better vulnerability scanning tools.

Deeper Dive into Out-of-Bounds Write Mechanics

Let’s explore this concept further. An out-of-bounds write, as in CVE-2025-43300, occurs when code like this (in pseudocode) happens:

buffer = allocate_memory(100); // Buffer for 100 bytes
write_to_buffer(buffer, index=101, data); // Index 101 is out of bounds

Without checking if index <= 99, it writes beyond the buffer, corrupting adjacent memory.

In Apple’s case, this ties to image file parsing. Images have headers and data sections; a malicious file might have oversized or malformed sections that trick the parser into writing extra data.

You might wonder, “Why don’t systems always check bounds?” It’s often a trade-off for performance, but in security-critical areas like image processing, it’s essential.

Implications for Users and Developers

For everyday users: Be cautious with image attachments in emails or downloads. This vulnerability highlights why updating software is key, though no specific patch is mentioned here.

For developers: When building apps that handle images, always implement rigorous bounds checking. Libraries for image processing should be audited for such issues.

In the Nuclei context, this encourages community-driven security improvements.

More Questions You Might Have

Continuing our Q&A style:

What is KEV in the context of vulnerabilities?

KEV stands for Known Exploited Vulnerabilities, and True means this CVE is listed there.

How was CVE-2025-43300 discovered or reported?

The details point to a GitHub issue published on August 22, 2025, at 10:00:07 +08:00.

Can this affect my iPad specifically?

Yes, iPadOS 17.7.10 and 18.6.2 are affected.

Is there a reward for contributing to Nuclei templates?

Yes, through the Community Rewards Program, but only after validation. See the FAQ for details.

What if my template is rejected?

It could be due to incompleteness or using blocked protocols. Revise based on feedback.

How does improper bounds checking lead to remote exploitation?

By allowing a remote attacker to supply the malicious file, which when processed, triggers the write remotely.

Are there similar vulnerabilities in other OS?

The document focuses on Apple, so we stick to that.

Practical Advice for Handling Similar Vulnerabilities

Here’s a list of best practices:

• Regularly check for OS updates.
• Use antivirus software that scans images.
• Educate yourself on safe file handling.
• For researchers, engage in bug bounty programs like Nuclei’s.

Wrapping Up: Why This Matters

CVE-2025-43300 serves as a reminder of how even routine tasks like opening images can pose risks if software has flaws like out-of-bounds writes. By understanding the affected versions, the exploitation method, and how to contribute to detection tools, you’re better equipped.

If you have more questions, think about what else puzzles you—perhaps “How can I test for this on my device?” While direct testing requires the POC, it’s best left to experts in controlled environments.

This vulnerability, with its high severity and KEV status, underscores the importance of vigilant security practices.