CVE-2026-39840Public exploitNetwork attack vector

Stored CSS injection via unsanitized display parameters

Published Apr 7, 2026 · Updated Apr 7, 2026

CSS injection in Wikimedia Foundation MediaWiki Cargo before 3.8.7 allows remote authenticated users to alter rendered page styles. The calendar, BPMN, Gantt, and timeline formatters place size parameters into inline style attributes without restricting them to CSS dimensions. An attacker needs permission to save Cargo query wikitext, and a reader must load the affected page; injected styles can alter content or trigger browser requests to attacker-controlled URLs.

CVSS severity5.1
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CSS injection in Wikimedia Foundation MediaWiki Cargo before 3.8.7 allows remote authenticated users to alter rendered page styles. The calendar, BPMN, Gantt, and timeline formatters place size parameters into inline style attributes without restricting them to CSS dimensions. An attacker needs permission to save Cargo query wikitext, and a reader must load the affected page; injected styles can alter content or trigger browser requests to attacker-controlled URLs.

The record

CVE
CVE-2026-39840
Published
Apr 7, 2026
Updated
Apr 7, 2026
Vendor
Wikimedia Foundation
Product
MediaWiki Cargo
Classifications
CWE-79
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 7, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 7, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=0 <3.8.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Wikimedia Foundation · MediaWiki Cargoversion=0 <3.8.7

Published CVSS scores

5.1Wikimedia FoundationCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA: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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

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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