CVE-2015-8872 in dosfstools
Summary
by MITRE
The set_fat function in fat.c in dosfstools before 4.0 might allow attackers to corrupt a FAT12 filesystem or cause a denial of service (invalid memory read and crash) by writing an odd number of clusters to the third to last entry on a FAT12 filesystem, which triggers an "off-by-two error."
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Analysis
by VulDB Data Team • 08/22/2022
The vulnerability identified as CVE-2015-8872 represents a critical flaw in the dosfstools package affecting FAT12 filesystems prior to version 4.0. This issue resides within the set_fat function located in the fat.c source file, demonstrating a classic example of improper input validation and memory handling that can lead to severe system instability. The flaw specifically targets the third to last entry in FAT12 filesystems when an odd number of clusters is written, creating a scenario where the system's memory management becomes corrupted due to incorrect boundary calculations.
The technical root cause of this vulnerability stems from an off-by-two error, which is classified under CWE-129 as an insufficient input validation or improper handling of buffer boundaries. When the set_fat function processes filesystem entries, it fails to properly account for the specific constraints of FAT12's three-byte cluster entries, leading to memory corruption when odd cluster counts are written to the designated memory locations. This error manifests as an invalid memory read operation that can result in system crashes or complete denial of service conditions, effectively rendering the affected filesystem inaccessible to legitimate users.
The operational impact of this vulnerability extends beyond simple system instability, as it can be exploited to cause complete filesystem corruption or unauthorized denial of service attacks against systems relying on FAT12 formatted storage devices. Attackers can leverage this flaw by crafting specific filesystem modifications that target the third to last entry in FAT12 partitions, making it particularly dangerous for embedded systems, removable media, and devices that frequently update filesystem metadata. The vulnerability's exploitation requires minimal privileges and can be executed through normal filesystem operations, making it a significant concern for system administrators managing legacy FAT12 environments.
From a cybersecurity perspective, this vulnerability aligns with ATT&CK technique T1490, which involves data destruction or corruption through filesystem manipulation. The flaw represents a classic case of memory safety issues that can be mitigated through proper bounds checking and input validation. System administrators should prioritize updating to dosfstools version 4.0 or later, which includes corrected boundary handling for FAT12 filesystem entries. Additionally, implementing monitoring solutions that detect unusual filesystem modification patterns can help identify potential exploitation attempts. The vulnerability highlights the importance of thorough testing for edge cases in filesystem utilities and demonstrates how seemingly minor implementation errors can lead to significant security implications, particularly in storage management software that operates at low system levels where memory corruption can have cascading effects throughout the operating system.