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CVE-2020-9054

Zyxel Multiple Network-Attached Storage (NAS) Devices

Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server doe...

CVSS
9.8
EPSS
100.0%
100.0% percentile
CISA KEV
Listed
Published
2020.03.05
PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV
Exploit probability100.0%
Technical severityCVSS 9.8

Vulnerability overview

Multiple ZyXEL network-attached storage (NAS) devices running firmware version 5.21 contain a pre-authentication command injection vulnerability, which may allow a remote, unauthenticated attacker to execute arbitrary code on a vulnerable device. ZyXEL NAS devices achieve authentication by using the weblogin.cgi CGI executable. This program fails to properly sanitize the username parameter that is passed to it. If the username parameter contains certain characters, it can allow command injection with the privileges of the web server that runs on the ZyXEL device. Although the web server doe...

Affected product and versions

Product
Zyxel Multiple Network-Attached Storage (NAS) Devices
Affected versions
V5.21(AAZF.7)C0, V5.21(AASZ.3)C0, V5.21(AATB.4)C0, V5.21(ABAG.4)C0, all, V4.75(AALH.2)C0, V4.75(AANV.2)C0, V4.81(AAAJ.1)C0, V4.81(AALS.1)C0, < 5.21\(aazf.7\)c0, < 5.21\(aasz.3\)c0, < 5.21\(aatb.4\)c0, < 5.21\(abag.4\)c0, >= 4.35 < 4.35\(abps.3\)c0, >= 4.35 < 4.35\(abfw.3\)c0, >= 4.35 < 4.35\(abfu.3\)c0, >= 4.35 < 4.35\(abiq.3\)c0, >= 4.35 < 4.35\(abaq.3\)c0, >= 4.35 < 4.35\(abar.3\)c0, >= 4.35 < 4.35\(aala.3\)c0
Fixed versions
5.21\(aazf.7\)c0, 5.21\(aasz.3\)c0, 5.21\(aatb.4\)c0, 5.21\(abag.4\)c0, 4.35\(abps.3\)c0, 4.35\(abfw.3\)c0, 4.35\(abfu.3\)c0, 4.35\(abiq.3\)c0, 4.35\(abaq.3\)c0, 4.35\(abar.3\)c0, 4.35\(aala.3\)c0, 4.35\(aalb.3\)c0, 4.35\(aaky.3\)c0, 4.35\(aakz.3\)c0, 4.35\(aaph.3\)c0, 4.35\(aapi.3\)c0, 4.35\(aapj.3\)c0, 4.35\(aapk.3\)c0, 4.35\(aapl.3\)c0, 4.35\(abae.3\)c0

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide
CISA required action

Apply updates per vendor instructions.

Due date: 2022.04.15
  1. 1
    Identify

    Confirm that Zyxel Multiple Network-Attached Storage (NAS) Devices and an affected version are present.

  2. 2
    Prioritize

    Combine exploitation signals with asset exposure and business criticality.

  3. 3
    Remediate

    Follow the vendor advisory or supported update path and preserve rollback options.

  4. 4
    Verify

    Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CWE
CWE-78
KEV added
2022.03.25
Ransomware use
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