CVE-2026-35544 Roundcube Webmail: Insufficient CSS sanitization in HTML e-mail messages
Attackers can bypass CSS sanitization in Roundcube Webmail using !important rules, potentially enabling UI redressing or content spoofing attacks.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-35544?
CVE-2026-35544 is a medium-severity 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 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.
Weakness: CWE-669
Which versions are affected by CVE-2026-35544?
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-2026-35544?
Upgrade roundcube/roundcubemail to 1.7-rc5 or later.
Is CVE-2026-35544 being exploited?
There is no known exploitation of CVE-2026-35544 in the wild and no public exploit code.
Other vulnerabilities in Roundcube Webmail
Sources
Also known as DEBIAN-CVE-2026-35544, GHSA-xpqh-grpw-4xmg, UBUNTU-CVE-2026-35544.