Description
Roundcube Webmail before 1.6.20 and 1.7.x before 1.7.5 is affected by a CSS scoping bypass in HTML messages. rcube_utils::mod_css_styles() did not treat an at-rule prologue such as @layer a; as a selector boundary, and did not handle selectors beginning with ::, so selectors following an at-rule were left unscoped and applied to the whole Roundcube interface instead of being confined to the message body. This allows an HTML message to restyle application chrome for UI redressing and spoofing. Upstream fixed this in the commit “Fix CSS scoping bypass in HTML messages using at-rules”.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Roundcube | Webmail | 1.6.0 – < 1.6.20, 1.7.0 – < 1.7.5 | 1.6.20 |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | roundcube | 1.6.20+dfsg-1 | — |
| Debian 13 | roundcube | 1.6.20+dfsg-0+deb13u1 | — |
| Debian 12 | roundcube | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | roundcube | No fix yet | — |
Show 6 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 26.04 LTS | roundcube | No fix yet | — |
| Ubuntu Pro 24.04 LTS | roundcube | No fix yet | — |
| Ubuntu Pro 22.04 LTS | roundcube | No fix yet | — |
| Ubuntu Pro 20.04 LTS | roundcube | No fix yet | — |
| Ubuntu Pro 18.04 LTS | roundcube | No fix yet | — |
| Ubuntu Pro 16.04 LTS | roundcube | No fix yet | — |
Advisories 1
- WID-SEC-2026-4043 Roundcube Webmail: Mehrere Schwachstellen BSI CERT-Bund (WID) · Nov 5, 2026
References
- https://bugs.debian.org/1151279 issue-tracking third-party-advisory
- https://github.com/roundcube/roundcubemail/commit/95b81ae12e2819a9b7e8636b5859b6244cda383e patch
- https://roundcube.net/news/2026/10/19/security-updates-1.6.20-and-1.7.5 vendor-advisory release-notes
- https://github.com/roundcube/roundcubemail/releases/tag/1.7.5 release-notes patch
- https://github.com/roundcube/roundcubemail/releases/tag/1.6.20 release-notes patch
- https://github.com/roundcube/roundcubemail/commit/ff9cf4a9bf3b7c66db9afe43fe5f1cc73b47ed35 patch