CVE-2017-18921Public exploitNetwork attack vector

Cross-site scripting via unsanitized error-page link

Published Jun 19, 2020 · Updated Aug 5, 2024

Cross-site scripting in Mattermost Server 3.5.1 and earlier allows remote attackers to execute script via a crafted error-page link. The error page copies the untrusted link query parameter into a return-link href without rejecting data URI payloads that contain script. Exploitation requires a victim to visit the crafted error page and open its return link in a new tab or window, allowing script execution in the Mattermost origin without reported session-cookie theft.

CVSS severity6.1
Medium
EPSS probability0.69%
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 Mattermost Server 3.5.1 and earlier allows remote attackers to execute script via a crafted error-page link. The error page copies the untrusted link query parameter into a return-link href without rejecting data URI payloads that contain script. Exploitation requires a victim to visit the crafted error page and open its return link in a new tab or window, allowing script execution in the Mattermost origin without reported session-cookie theft.

The record

CVE
CVE-2017-18921
Published
Jun 19, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-79, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 19, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 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

4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
6.1NVDCVSS: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')
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

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Your stack

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