CVE-2021-35027Network attack vector

Sensitive file disclosure via unfiltered dot-dot sequences

Published Sep 29, 2021 · Updated Aug 4, 2024

Directory traversal in the web server of Zyxel ZyWALL VPN2S Firmware 1.12 allows remote attackers to read sensitive data via a crafted URL. The zhttpd web server accepts dot-dot character sequences without adequate URL sanitization, allowing the resolved path to leave its intended directory. No authentication or user interaction is required, and the documented consequence is limited to disclosure of files accessible to the web server.

CVSS severity7.5
High
EPSS probability2.04%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Directory traversal in the web server of Zyxel ZyWALL VPN2S Firmware 1.12 allows remote attackers to read sensitive data via a crafted URL. The zhttpd web server accepts dot-dot character sequences without adequate URL sanitization, allowing the resolved path to leave its intended directory. No authentication or user interaction is required, and the documented consequence is limited to disclosure of files accessible to the web server.

The record

CVE
CVE-2021-35027
Published
Sep 29, 2021
Updated
Aug 4, 2024
Vendor
Zyxel Networks
Product
ZyWALL VPN2S Firmware
Classifications
CWE-27, CWE-22, T1190
Attack vector
network
Privileges
unauthenticated

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 vectornetwork
Required privilegesunauthenticated

What is affected?

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

Published CVSS scores

7.5Zyxel CorporationCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NISTAV:N/AC:L/Au:N/C:P/I:N/A:N

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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-27Path Traversal: 'dir/../../filename'
CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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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