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Roundcube Webmail CVE-2026-9818

| EUVD-2026-32893 MEDIUM
Incomplete List of Disallowed Inputs (CWE-184)
2026-05-28 OCD GHSA-mhgj-jxxf-gxj9
Information Disclosure
4.7
CVSS 3.1
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CVSS VectorNVD

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

Lifecycle Timeline

2
Source Code Evidence Fetched
May 28, 2026 - 13:21 vuln.today
Analysis Generated
May 28, 2026 - 13:21 vuln.today

DescriptionNVD

Roundcube's HTML sanitization path for message rendering allows loopback, localhost, RFC1918, link-local, and ULA URLs even when remote content loading is disabled. A remote attacker can send an HTML email that causes the victim's browser to issue requests to local or private-network services simply by opening the message preview.

AnalysisAI

Roundcube Webmail's HTML sanitizer fails to block loopback, localhost, RFC1918, link-local, and ULA addresses when rendering HTML email, even when the user has disabled remote content loading. An unauthenticated remote attacker (PR:N per CVSS) can send a crafted HTML email that - upon the victim previewing it - causes their browser to issue HTTP requests to internal or private-network services, enabling blind probing or interaction with local infrastructure. …

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CVE-2026-9818 vulnerability details – vuln.today
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