CVE-2026-35540 Roundcube Webmail: Insufficient CSS sanitization in HTML e-mail messages
Attackers can exploit insufficient CSS sanitization in HTML emails to trigger SSRF or disclose information from local network hosts.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-35540?
CVE-2026-35540 is a medium-severity server-side request forgery vulnerability in Roundcube Webmail, published on 3 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
An issue was discovered in Roundcube Webmail 1.6.0 before 1.6.14. Insufficient Cascading Style Sheets (CSS) sanitization in HTML e-mail messages may lead to SSRF or Information Disclosure, e.g., if stylesheet links point to local network hosts.
Weakness: CWE-669
Which versions are affected by CVE-2026-35540?
2 open source packages ship an affected version, including roundcube/roundcubemail. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
roundcube/roundcubemail Packagist | From 1.7-beta | 1.7-rc5 |
roundcube/roundcubemail Packagist | From 1.7-beta | 1.7-rc5 |
Products include Roundcube Webmail.
How do I fix CVE-2026-35540?
Upgrade roundcube/roundcubemail to 1.7-rc5 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-35540 being exploited?
There is no known exploitation of CVE-2026-35540 in the wild and no public exploit code.
Other vulnerabilities in Roundcube Webmail
Sources
Also known as DEBIAN-CVE-2026-35540, GHSA-vxg2-hhgr-37fx, UBUNTU-CVE-2026-35540.