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Webmail EUVD-2026-18591

| CVE-2026-35544 MEDIUM
Incorrect Resource Transfer Between Spheres (CWE-669)
2026-04-03 mitre GHSA-xpqh-grpw-4xmg
Authentication Bypass Webmail
5.3
CVSS 3.1 · NVD
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Severity by source

NVD PRIMARY
5.3 MEDIUM
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Lifecycle Timeline

4
Patch released
Apr 04, 2026 - 08:30 nvd
Patch available
EUVD ID Assigned
Apr 03, 2026 - 04:30 euvd
EUVD-2026-18591
Analysis Generated
Apr 03, 2026 - 04:30 vuln.today
CVE Published
Apr 03, 2026 - 03:59 nvd
MEDIUM 5.3

DescriptionCVE.org

An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to a fixed-position mitigation bypass via the use of !important.

AnalysisAI

Roundcube Webmail before versions 1.5.14 and 1.6.14 allows unauthenticated remote attackers to bypass CSS-based security mitigations in HTML email rendering by injecting !important declarations, enabling potential integrity attacks such as phishing or UI redressing. The vulnerability stems from insufficient CSS sanitization when processing HTML email messages, with no authentication required and minimal attack complexity.

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Vulnerability AssessmentAI

Risk Assessment This vulnerability presents moderate real-world risk despite its modest CVSS score of 5.3. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker crafts a malicious HTML email containing CSS rules with !important declarations designed to override Roundcube's fixed-position security overlays. When a victim opens this email in Roundcube Webmail, the malicious CSS renders a fake login form or warning dialog on top of the legitimate email content, deceiving the user into clicking a phishing link or submitting credentials. …
Remediation Vendor-released patches are available for all affected versions: upgrade to Roundcube Webmail 1.5.14 or later in the 1.5.x branch, or 1.6.14 or later in the 1.6.x branch. … Detailed patch versions, workarounds, and compensating controls in full report.
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EUVD-2026-18591 vulnerability details – vuln.today
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