CVE-2021-40542Public exploitNetwork attack vector

Script execution via unencoded link_url reflection

Published Oct 11, 2021 · Updated Aug 4, 2024

Reflected cross-site scripting in OS4ED openSIS Classic 8.0 allows remote attackers to execute JavaScript through a crafted link_url value. Ajax_url_encode.php reads the link_url request parameter and echoes it into an HTML response without output encoding, so browser-interpreted markup runs in the victim's context. No authentication is required to create the URL, but a user must open it; exploitation permits script execution in that user's openSIS browser context.

CVSS severity6.1
Medium
EPSS probability3.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected cross-site scripting in OS4ED openSIS Classic 8.0 allows remote attackers to execute JavaScript through a crafted link_url value. Ajax_url_encode.php reads the link_url request parameter and echoes it into an HTML response without output encoding, so browser-interpreted markup runs in the victim's context. No authentication is required to create the URL, but a user must open it; exploitation permits script execution in that user's openSIS browser context.

The record

CVE
CVE-2021-40542
Published
Oct 11, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 11, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NIST NVDCVSS:3.1/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 exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1204.001User Execution: Malicious Link

Public exploit references

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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