CVE-2021-40084Public exploit

Command execution via shell eval of GECOS

Published Aug 25, 2021 · Updated Aug 4, 2024

Command injection in opensysusers 0.6 and earlier allows attackers to execute shell commands through a crafted sysusers.d GECOS field. The parse_string function passes configuration text to the shell eval builtin, causing metacharacters in GECOS data to execute instead of remaining literal. Exploitation requires a crafted sysusers.d file to be processed by opensysusers, and injected commands run with the invoking process's privileges.

CVSS severity9.8
Critical
EPSS probability2.71%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Command injection in opensysusers 0.6 and earlier allows attackers to execute shell commands through a crafted sysusers.d GECOS field. The parse_string function passes configuration text to the shell eval builtin, causing metacharacters in GECOS data to execute instead of remaining literal. Exploitation requires a crafted sysusers.d file to be processed by opensysusers, and injected commands run with the invoking process's privileges.

The record

CVE
CVE-2021-40084
Published
Aug 25, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-94, T1059.004
Attack vector
Unavailable
Privileges
Unavailable

Timeline

How it unfolded

  1. Aug 25, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorUnavailable in this record.
Required privilegesUnavailable in this record.

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P
9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
VectorUnavailable
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-94Improper Control of Generation of Code ('Code Injection')
T1059.004Unix Shell

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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