CVE-2021-35028

Authenticated command injection via CGI parameter filtering

Published Sep 29, 2021 · Updated Aug 4, 2024

Command injection in ZyWALL VPN2S Firmware 1.12 allows authenticated local users to execute arbitrary OS commands via a CGI program. The CGI program improperly filters input parameters before incorporating them into command execution, allowing shell metacharacters to alter the invoked command. Access requires an authenticated user on the local network or console path; successful exploitation can compromise confidentiality, integrity, and availability of the firewall.

CVSS severity7.8
High
EPSS probability0.30%
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 ZyWALL VPN2S Firmware 1.12 allows authenticated local users to execute arbitrary OS commands via a CGI program. The CGI program improperly filters input parameters before incorporating them into command execution, allowing shell metacharacters to alter the invoked command. Access requires an authenticated user on the local network or console path; successful exploitation can compromise confidentiality, integrity, and availability of the firewall.

The record

CVE
CVE-2021-35028
Published
Sep 29, 2021
Updated
Aug 4, 2024
Vendor
Zyxel Networks
Product
ZyWALL VPN2S Firmware
Classifications
CWE-78, T1059
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Sep 29, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.12(ABLN.0)C0

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Zyxel Networks · ZyWALL VPN2S Firmwareversion=1.12(ABLN.0)C0

Published CVSS scores

7.8NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.2NVDAV:L/AC:L/Au:N/C:C/I:C/A:C
7.3Zyxel CorporationCVSS:3.1/AV:A/AC:H/PR:H/UI:R/S:C/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 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-78Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
T1059Command and Scripting Interpreter

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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