CVE-2022-26531Public exploit

Memory corruption and crash via unchecked CLI arguments

Published May 24, 2022 · Updated Aug 3, 2024

Memory corruption in Zyxel appliance firmware allows local users to crash the system or corrupt process memory via crafted CLI input. The zysh handlers copy unchecked diagnostic, debug, and ssh arguments into fixed-size stack buffers and use network-tool extension text directly as an sprintf format string. Authenticated CLI access is required; the format-string path can leak stack data, crash zysh, or escape the restricted shell as the logged-in user.

CVSS severity6.1
Medium
EPSS probability5.67%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Memory corruption in Zyxel appliance firmware allows local users to crash the system or corrupt process memory via crafted CLI input. The zysh handlers copy unchecked diagnostic, debug, and ssh arguments into fixed-size stack buffers and use network-tool extension text directly as an sprintf format string. Authenticated CLI access is required; the format-string path can leak stack data, crash zysh, or escape the restricted shell as the logged-in user.

The record

CVE
CVE-2022-26531
Published
May 24, 2022
Updated
Aug 3, 2024
Vendor
Zyxel Networks
Product
Zyxel NAP203 Firmware
Classifications
CWE-20, T1203
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 24, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=<= 6.25(ABFA.7)

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

Zyxel Networks · Zyxel NAP203 Firmwareversion=<= 6.25(ABFA.7)
Zyxel Networks · USG FLEX Series Firmwareversion=4.50 through 5.21
Zyxel Networks · Zyxel NSG Series Firmwareversion=1.00 through 1.33 Patch 4
Zyxel Networks · WAC500 Firmwareversion=<= 6.30(ABVS.2)
Zyxel Networks · Zyxel NXC2500 Firmwareversion=<= 6.10(AAIG.3)
Zyxel Networks · WAX510D Firmwareversion=<= 6.30(ABTF.2)
Zyxel Networks · Zyxel ATP Series Firmwareversion=4.32 through 5.21
Zyxel Networks · NWA50AX Firmwareversion=<= 6.25(ABYW.5)
Zyxel Networks · Zyxel USG/ZyWALL Series Firmwareversion=4.09 through 4.71
Zyxel Networks · Zyxel VPN Series Firmwareversion=4.30 through 5.21

Published CVSS scores

7.8NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.1Zyxel CorporationCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:H
4.6NIST NVDAV:L/AC:L/Au:N/C:P/I:P/A:P

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 exploitPublished

Weakness, pattern, technique

CWE-20Improper Input Validation
T1203Exploitation for Client Execution

Public exploit references

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

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo