CVE-2026-35539 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in roundcube/roundcubemail. A fix is available for roundcube/roundcubemail — see the affected versions and patch details below.
Roundcube Webmail: Insufficient HTML attachment sanitization in preview mode
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-35539.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
roundcube/roundcubemailReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | roundcube/roundcubemail | ≥ 1.7-beta&&< 1.7-rc5 | 1.7-rc5composer require roundcube/roundcubemail:^1.7-rc5 |
Affected Products
webmailroundcubeDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for roundcube/roundcubemail, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update roundcube/roundcubemail to 1.7-rc5 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-35539 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-35539 in your dependencies?
Find it across Packagist, including transitive dependencies.