NTFS-3G Heap Buffer Overflow Vulnerability (CVE-2026-40706)

CVE-2026-40706 describes a heap buffer overflow vulnerability affecting NTFS-3G, specifically versions 2022.10.3 and earlier, before the patch in version 2026.2.25. The vulnerability lies within the ntfs_build_permissions_posix() function in acls.c. An attacker can exploit this flaw by creating a malicious NTFS image. When the affected software attempts to read this specially crafted image, a heap buffer overflow occurs. This is triggered when the software processes a security descriptor containing multiple ACCESS_DENIED Access Control Entries (ACEs), each including WRITE_OWNER permissions, and originating from distinct group Security Identifiers (SIDs). Successful exploitation allows an attacker to corrupt heap memory within the SUID-root ntfs-3g binary, potentially leading to privilege escalation or arbitrary code execution.

Attack Chain

1. Attacker crafts a malicious NTFS image containing a specially designed security descriptor.
2. The security descriptor includes multiple ACCESS_DENIED ACEs.
3. Each ACE within the descriptor contains WRITE_OWNER permissions.
4. The ACEs originate from distinct group SIDs, triggering the overflow condition.
5. The attacker delivers the malicious NTFS image to a system running a vulnerable version of NTFS-3G. This may occur through physical media or network shares.
6. The victim system attempts to read the malicious NTFS image using a vulnerable NTFS-3G version, such as during a stat, readdir, or open operation.
7. The ntfs_build_permissions_posix() function is called to process the security descriptor.
8. The heap buffer overflow occurs during the processing of the malicious ACEs, corrupting heap memory. This can lead to denial of service or potentially arbitrary code execution.

Impact

Successful exploitation of CVE-2026-40706 allows for heap memory corruption in the ntfs-3g binary, which runs with elevated privileges due to its SUID-root configuration. The observed consequence is memory corruption. Depending on the extent of the corruption, this could lead to denial-of-service or arbitrary code execution. Given the wide usage of NTFS-3G for mounting NTFS volumes on Linux and other systems, a successful exploit could affect a large number of systems.

Recommendation

• Upgrade NTFS-3G to version 2026.2.25 or later to patch CVE-2026-40706 (reference: https://github.com/tuxera/ntfs-3g/releases/tag/2026.2.25).
• Monitor systems for unexpected crashes or errors related to ntfs-3g operations, which may indicate exploitation attempts. Deploy the Sigma rules below to your SIEM and tune for your environment.
• Consider implementing stricter access controls and validation measures on NTFS images to prevent the use of malicious images (mitigation based on the vulnerability description).