CVE-2026-40878Public exploitNetwork attack vector

Unauthenticated phishing via wrong-context Twig escaping

Published Apr 21, 2026 · Updated Apr 21, 2026

Cross-site scripting in the mailcow: dockerized web interface before 2026-03b allows remote attackers to inject login-page parameters. The setLang() helper places raw REQUEST_URI data in a JavaScript string using HTML escaping, while query_string() preserves attacker-controlled GET parameters in language links. A victim must open a crafted link; typical deployments block direct script execution, but the injection enables phishing and can disable login-page JavaScript behind URL-decoding proxies.

CVSS severity2.1
Low
EPSS probability0.80%
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 the mailcow: dockerized web interface before 2026-03b allows remote attackers to inject login-page parameters. The setLang() helper places raw REQUEST_URI data in a JavaScript string using HTML escaping, while query_string() preserves attacker-controlled GET parameters in language links. A victim must open a crafted link; typical deployments block direct script execution, but the injection enables phishing and can disable login-page JavaScript behind URL-decoding proxies.

The record

CVE
CVE-2026-40878
Published
Apr 21, 2026
Updated
Apr 21, 2026
Vendor
mailcow
Product
mailcow: dockerized
Classifications
CWE-79
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 21, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 21, 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=< 2026-03b

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

mailcow · mailcow: dockerizedversion=< 2026-03b

Published CVSS scores

2.1GitHub, Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:L/VI:L/VA:L/SC:N/SI:N/SA: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.

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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')

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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