CVE-2021-20857Network attack vector

Unauthenticated browser script execution via undisclosed input path

Published Dec 1, 2021 · Updated Aug 3, 2024

Cross-site scripting in ELECOM LAN Routers running firmware 1.20 and earlier allows remote attackers to execute script in a logged-in user's browser. ELECOM and JVN have not published the affected management-page field or how untrusted input reaches browser output without safe encoding. Exploitation requires LAN-side access and a logged-in user to load attacker-controlled content; the documented impact is script execution in that browser.

CVSS severity6.1
Medium
EPSS probability0.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cross-site scripting in ELECOM LAN Routers running firmware 1.20 and earlier allows remote attackers to execute script in a logged-in user's browser. ELECOM and JVN have not published the affected management-page field or how untrusted input reaches browser output without safe encoding. Exploitation requires LAN-side access and a logged-in user to load attacker-controlled content; the documented impact is script execution in that browser.

The record

CVE
CVE-2021-20857
Published
Dec 1, 2021
Updated
Aug 3, 2024
Vendor
ELECOM CO., LTD.
Product
ELECOM LAN Routers
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 1, 2021CVE 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=WRC-2533GHBK-I firmware v1.20 and prior

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ELECOM CO., LTD. · ELECOM LAN Routersversion=WRC-2533GHBK-I firmware v1.20 and prior

Published CVSS scores

2.6JPCERT/CC and IPAAV:N/AC:H/Au:N/C:N/I:P/A:N
3.5NIST NVDAV:N/AC:M/Au:S/C:N/I:P/A:N
5.4NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
6.1JPCERT/CC and IPACVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/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-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1203Exploitation for Client Execution

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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