CVE-2026-103010

Heap-based Buffer Overflow in hMailServer

Published Oct 8, 2026 CVSS 3.1 · 7.8 High EPSS < 1% KEV · Not listed
Description
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.

Remediation

Vendor Solution

Upgrade to hMailServer 6.3.6, which also requires authentication for the COM Utilities helpers (6.3.4 is the first release with this routine fixed).

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Progressive Robot
Progressive Robot hmailserver
Vendors & Products Progressive Robot
Progressive Robot hmailserver
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Heap-based Buffer Overflow in hMailServer
Weaknesses CWE-122
References
Metrics cvssV3_1

{'score': 7.8, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitLab
Published
Updated
Oct 8, 2026, 2:22 PM
Reserved
Sep 29, 2026, 9:04 PM
Status
Deferred
Published
Oct 8, 2026, 11:16 AM
Modified
Oct 8, 2026, 9:02 PM