CVE-2015-8026 in exfat-utils
Summary
by MITRE
Heap-based buffer overflow in the verify_vbr_checksum function in exfatfsck in exfat-utils before 1.2.1 allows remote attackers to cause a denial of service (infinite loop) or possibly execute arbitrary code via a crafted filesystem.
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Analysis
by VulDB Data Team • 11/22/2022
The vulnerability identified as CVE-2015-8026 represents a critical heap-based buffer overflow within the exfatfsck utility, specifically in the verify_vbr_checksum function of the exfat-utils package. This flaw exists in versions prior to 1.2.1 and presents a significant security risk to systems utilizing exFAT filesystems. The vulnerability stems from inadequate input validation and memory management practices within the filesystem checking utility, which is designed to verify and repair exFAT filesystem structures. When processing maliciously crafted filesystem images, the utility fails to properly bounds-check memory allocations, leading to potential memory corruption that can manifest in unpredictable system behavior.
The technical exploitation of this vulnerability occurs when a remote attacker crafts a specially formatted exFAT filesystem image that triggers the buffer overflow condition within the verify_vbr_checksum function. This function is responsible for validating the volume boot record checksums of exFAT filesystems, which are critical structural elements that define filesystem parameters and metadata. The heap-based nature of the overflow indicates that the vulnerability affects dynamically allocated memory regions, making it particularly dangerous as it can lead to memory corruption that may be leveraged for code execution. The infinite loop condition mentioned in the vulnerability description suggests that the malformed input causes the utility to enter a state where it repeatedly processes corrupted data without proper termination conditions, effectively exhausting system resources and causing denial of service.
The operational impact of CVE-2015-8026 extends beyond simple denial of service scenarios, as the vulnerability may potentially enable arbitrary code execution on affected systems. When exploited successfully, this buffer overflow could allow attackers to execute malicious code with the privileges of the exfatfsck process, which typically runs with elevated permissions during filesystem verification operations. The vulnerability's remote exploitation capability means that attackers do not need physical access to the target system, making it particularly dangerous in networked environments where filesystem images might be processed automatically by system services or user applications. Systems that automatically mount or verify exFAT filesystems, including those in cloud environments, mobile devices, or automated backup systems, would be at risk when encountering maliciously crafted filesystem images.
Mitigation strategies for this vulnerability should focus on immediate patching of affected systems with exfat-utils version 1.2.1 or later, which contains the necessary fixes to prevent the buffer overflow condition. Organizations should also implement proper input validation and sanitization measures when processing filesystem images, particularly in automated environments where untrusted data might be encountered. The vulnerability aligns with CWE-121, heap-based buffer overflow, and demonstrates characteristics consistent with attack patterns found in the MITRE ATT&CK framework under the T1059.007 technique for command and scripting interpreter execution. Network administrators should monitor for suspicious filesystem image processing activities and consider implementing filesystem verification restrictions to prevent automatic processing of untrusted exFAT images. Additionally, system hardening measures including stack canaries, address space layout randomization, and non-executable stack protections should be considered as additional defensive measures against potential exploitation of this and similar buffer overflow vulnerabilities.