What is CVE-2020-35730?

CVE-2020-35730 is a medium-severity vulnerability in Roundcube Webmail, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2020-12-28.

How severe is CVE-2020-35730?

Medium severity. CVSS v3 base score is 6.1 out of 10.

Is CVE-2020-35730 known to be exploited?

Yes. CVE-2020-35730 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-22), indicating it is being actively exploited. 9 public proof-of-concept repositories are indexed.

XSS in Roundcube Webmail

CVE-2020-35730

An XSS issue was discovered in Roundcube Webmail before 1.2.13, 1.3.x before 1.3.16, and 1.4.x before 1.4.10. The attacker can send a plain text e-mail message, with JavaScript in a link reference element that is mishandled by linkref_addindex in rcube_string_replacer.php.

Vulnerability class: XSS (Cross-Site Scripting)

Published 2020-12-28 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 6.1 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N.

EPSS exploit prediction

EPSS: 0.329 (98.3th percentile), scored 2026-10-18.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 98th percentile — 98.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.327 · newest: 0.329 · change: +0.002

Affected products

Roundcube Webmail
Debian Linux — versions 9.0
Fedoraproject Fedora — versions 32, 33

Weakness classification (CWE)

CWE-79 — Cross-site Scripting

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2023-06-22. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2023-07-13.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

roundcube.net/download/ (Product)
github.com/roundcube/roundcubemail/compare/1.4.9...1.4.10 (Patch)
bugs.debian.org/cgi-bin/bugreport.cgi (Mailing List, Issue Tracking)
www.alexbirnberg.com/roundcube-xss.html (Broken Link)
github.com/roundcube/roundcubemail/releases/tag/1.4.10 (Release Notes)
github.com/roundcube/roundcubemail/releases/tag/1.3.16 (Release Notes)
github.com/roundcube/roundcubemail/releases/tag/1.2.13 (Release Notes)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory, Mailing List, Release Notes)
lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/… (vendor-advisory, Mailing List, Release Notes)
134c704f-9b21-4f2e-91b3-4a467353bcc0 (US Government Resource)

Frequently asked questions

What is CVE-2020-35730?: CVE-2020-35730 is a medium-severity vulnerability in Roundcube Webmail, classified under Cross-site Scripting. CVSS score: 6.1/10. Published 2020-12-28.
How severe is CVE-2020-35730?: Medium severity. CVSS v3 base score is 6.1 out of 10.
Is CVE-2020-35730 known to be exploited?: Yes. CVE-2020-35730 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-22), indicating it is being actively exploited. 9 public proof-of-concept repositories are indexed.