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CVE-2021-20617

44
FAUCET Score

CVE-2021-20617 is a critical improper access control vulnerability affecting acmailer versions 4.0.1 and earlier, and acmailer DB versions 1.1.3 and earlier. This flaw allows unauthenticated remote attackers to execute arbitrary OS commands or gain administrative privileges, potentially leading to the compromise of sensitive server information. With a CVSS score of 9.8 (CRITICAL) and an EPSS score indicating high exploitability, this vulnerability poses a significant risk due to its low attack complexity and severe impact on confidentiality, integrity, and availability. While not listed on CISA's KEV catalog and lacking Metasploit or ExploitDB entries, Nuclei templates exist for detecting and exploiting this vulnerability, suggesting potential for active exploitation despite minimal community discussion or media coverage.

Impacted Technologies

VendorProductVersion(s)CPE
<= 4.0.1CPE matchmatch criteria
cpe:2.3:a:acmailer:acmailer:*:*:*:*:*:*:*:*
<= 1.1.3CPE matchmatch criteria
cpe:2.3:a:acmailer:acmailer_db:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

9.8CRITICAL

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

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
HIGH
Integrity Impact
HIGH
Availability Impact
HIGH
Exploitability Score
3.9
Impact Score
5.9
CvssVersion
3.1

Exploit Intelligence

EPSS Score
7.87%
Probability of exploitation in next 30 days
EPSS Percentile
94.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
Nuclei: CVE-2021-20617 · Dec 13, 2025
This CVE's current EPSS score of 0.0787 is in the 89th percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

jvn.jp / en/jp/JVN35906450/index.html
Third Party Advisory
acmailer.jp / info/de.cgi
Vendor Advisory