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Heap overflow and endless loop in exfatfsck / exfat-utils

exfat-utils is a collection of tools to work with the exFAT filesystem. Fuzzing the exfatfsck with american fuzzy lop led to the discovery of a write heap overflow and an endless loop.

Especially at risk are systems that are configured to run filesystem checks automatically on external devices like USB flash drives.

A malformed input can cause a write heap overflow in the function verify_vbr_checksum. It might be possible to use this for code execution.
Upstream bug report
Sample file triggering the bug
Git commit for fix

Another malformed input can cause an endless loop, leading to a possible denial of service.
Upstream bug report
Sample file triggering the bug
Git commit of fix

Both issues have been fixed in the latest release 1.2.1 of exfat-utils.


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