Heap-based Buffer Overflow in hMailServer

Heap-based buffer overflow in the legacy Blowfish decryption routine (BlowFishEncryptor::DecryptFromString) in Progressive Robot hMailServer 6.0.0 through 6.3.3 on Windows allows a local interactive user with no hMailServer credentials to write bytes of their choosing past the end of a 255-byte heap buffer in the hMailServer service process, which runs as LocalSystem by default. The user does this by passing a long hexadecimal string to the COM method Utilities.BlowfishDecrypt, which checked no authentication. The routine converted hexadecimal input of any length into a fixed 255-byte buffer before decrypting it in place. The result is a denial of service (service crash), and possibly code execution with the privileges of the service account.

Source published

8 Oct 2026 10:53:10 UTC

Source modified

8 Oct 2026 14:22:28 UTC

Observed here

23 Oct 2026 15:48:27 UTC

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CVSS 3.1 · 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H