Executive Summary

This vulnerability is a NULL pointer dereference in the ext4_dir_en_get_name_len function within the lwext4 1.0.0 codebase. It occurs because the function does not properly validate directory entry pointers before accessing the name_len field during directory iteration. An attacker can exploit this by providing a specially crafted EXT4 filesystem image with malformed directory entries, which causes the program to attempt to access invalid memory, leading to a segmentation fault.

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Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS). By exploiting the NULL pointer dereference, an attacker can cause the affected software to crash or become unresponsive when processing a malicious EXT4 filesystem image. This can disrupt normal operations and availability of systems relying on the vulnerable lwext4 library.

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Compliance Impact

The vulnerability CVE-2025-70099 causes a denial of service (DoS) by triggering a NULL pointer dereference in the lwext4 library when processing malformed EXT4 filesystem images. It does not involve unauthorized access, data leakage, or modification of data.

Since the vulnerability results in availability impact only (denial of service) without compromising confidentiality or integrity, its direct effect on compliance with standards like GDPR or HIPAA—which primarily focus on protecting personal data confidentiality and integrity—is limited.

However, denial of service conditions can indirectly affect compliance if they disrupt access to critical systems or data required for regulatory obligations, such as timely access to personal health information under HIPAA or data subject rights under GDPR.

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Detection Guidance

This vulnerability can be detected by reproducing the crash condition using fuzz testing tools that process ext4 filesystem images. Specifically, the vulnerability was discovered using AddressSanitizer during fuzz testing with the afl_ext4_mount_read tool and a crafted test case named sig11_2_1_lwext4_ext4_dir_h_126.

To detect the vulnerability on your system, you can attempt to mount or read specially crafted EXT4 filesystem images that contain malformed directory entries and observe if the lwext4 library crashes with a segmentation fault.

Suggested command example to test the vulnerability (assuming you have the afl_ext4_mount_read tool and the test case file):

• afl_ext4_mount_read sig11_2_1_lwext4_ext4_dir_h_126

This command attempts to mount/read the malformed EXT4 image and will likely trigger the NULL pointer dereference if the system is vulnerable.

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Mitigation Strategies

Immediate mitigation steps include avoiding the use or mounting of untrusted or specially crafted EXT4 filesystem images that could trigger the NULL pointer dereference.

Since the vulnerability causes a denial of service by crashing the lwext4 library during directory iteration, restricting access to potentially malicious EXT4 images and applying patches or updates to the lwext4 library when available are critical.

If a patch or updated version of lwext4 addressing this issue is released, promptly update to that version to prevent exploitation.

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