# CVE-2021-20617: Acmailer - RCE

> Live exploitation tracking for CVE-2021-20617 by the CrowdSec Live Exploit Tracker, built from real-world attack data crowdsourced from CrowdSec's global network.

Page: https://tracker.crowdsec.net/cves/CVE-2021-20617

## Key facts

- **Exploitation phase:** Limited Exploitation. The vulnerability is known but shows very limited attacker interest or exploitation activity.
- **CVSS score:** 9.8
- **Public exploit available:** Yes
- **Affected products:** Seeds Co.,Ltd. acmailer and acmailer DB
- **Tags:** web_application

## Description

Improper access control vulnerability in acmailer ver. 4.0.1 and earlier, and acmailer DB ver. 1.1.3 and earlier allows remote attackers to execute an arbitrary OS command, or gain an administrative privilege which may result in obtaining the sensitive information on the server via unspecified vectors.

## CrowdSec analysis

[CVE-2021-20617](https://euvd.enisa.europa.eu/vulnerability/CVE-2021-20617) is a critical improper access control vulnerability in acmailer and acmailer DB that allows remote attackers to execute arbitrary OS commands or escalate privileges to gain administrative access. Exploiting this flaw could enable attackers to obtain sensitive information from the server or fully compromise the affected system.

CrowdSec has been tracking this vulnerability and its exploits since 7th of January 2026.

CrowdSec network observations suggest that most exploitation of CVE-2021-20617 involves focused reconnaissance to identify viable targets. Attackers typically tailor their campaigns based on system exposure and configuration. It is unlikely that a given attack is accidental.
CrowdSec network telemetry also shows that exploitation of CVE-2021-20617 has significantly declined over the past week. Attack volumes are well below the long-term average, suggesting attackers are rapidly losing interest. The vulnerability appears to be falling out of active use across most threat landscapes.

Attackers exploit the `/init_ctl.cgi` endpoint by injecting OS commands into the `sendmail_path` parameter, enabling remote code execution and potential privilege escalation.

## Timeline

- 2021-01-14: CVE Published. CVE-2021-20617 is published to NVD.
- 2026-01-07: Rule Released. CrowdSec releases a rule to detect CVE-2021-20617 exploitation attempts against the CrowdSec Network.
- 2026-01-14: CrowdSec First Seen. CrowdSec observes in-the-wild exploitation of CVE-2021-20617 for the first time.

## References

- https://jvn.jp/en/jp/JVN35906450/index.html
- https://www.acmailer.jp/info/de.cgi?id=101
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2021/CVE-2021-20617.yaml

## Live exploitation data

The [Live Exploit Tracker page](https://tracker.crowdsec.net/cves/CVE-2021-20617) follows observed exploitation activity for CVE-2021-20617. [Request an API key](https://tracker.crowdsec.net/request-api-key) for full access to its exploitation timeline, attacking IP addresses and blocklists.