What is CVE-2026-35540?

CVE-2026-35540 is a medium-severity vulnerability in Roundcube Webmail, classified under Incorrect Resource Transfer Between Spheres. CVSS score: 5.4/10. Published 2026-04-03.

How severe is CVE-2026-35540?

Medium severity. CVSS v3 base score is 5.4 out of 10.

Vulnerability in Roundcube Webmail

CVE-2026-35540

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.

EPSS: 0.003 (23.4th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N.

Affected products

Roundcube Webmail — versions 1.6.0

Weakness classification (CWE)

CWE-669 — Incorrect Resource Transfer Between Spheres

References

cve@mitre.org (Vendor Advisory)
cve@mitre.org (Release Notes)
cve@mitre.org (Patch)
cve@mitre.org (Release Notes)
cve@mitre.org (Patch)

Frequently asked questions

What is CVE-2026-35540?: CVE-2026-35540 is a medium-severity vulnerability in Roundcube Webmail, classified under Incorrect Resource Transfer Between Spheres. CVSS score: 5.4/10. Published 2026-04-03.
How severe is CVE-2026-35540?: Medium severity. CVSS v3 base score is 5.4 out of 10.