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CISA KEV · ACTIVELY EXPLOITED
MEDIUM severity

CVE-2020-35730 — roundcubemail

MEDIUM

CVE-2020-35730 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability. It is in CISA's Known Exploited Vulnerabilities catalog (added 2023-06-22) — treat it as actively exploited and patch now. A fix is available — see the affected versions and patch details below.

Also known asBIT-roundcube-2020-35730
Published
Updated
Affected
3 products
Patched
See advisory
Exploits
1 known
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, CISA KEV, FIRST.org (EPSS)

Exploitation Status

Actively exploited in the wild

  • Confirmed by CISA's Known Exploited Vulnerabilities catalog on 2023-06-22. Federal agencies were required to remediate by 2023-07-13.

Exploitation and automatability from CISA (KEV catalog and SSVC triage) for CVE-2020-35730.

EPSS Exploitation Probability

via FIRST.org ↗
32.9%probability of exploitation in next 30 days
Moderate Risk+0.23%
Lower risk than most CVEs98th percentile — riskier than 98% of all scored CVEsHighest risk
22.3%40.8%59.3%77.8%64.8%32.9%Apr 26Aug 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-35730 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Counts from FIRST.org, log-scaled.

Description

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.

Affected Products

3 products · 6 configurations
OS
debian linuxdebian
1 version
9.0
OS
fedorafedoraproject
2 versions
3233
Application
webmailroundcube
≥ 1.4 && < 1.4.10
range
Exploits & PoCs
1

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

An XSS issue was discovered in Roundcube Webmail before 1.2.13, 1.3.x be…

cisa.govCISAJun 2023

Detection & mitigation playbook

Vulnerability

  1. Detect

    Identify every host running the affected component and compare the installed build against the fixed version below — for source-built or distro-packaged software the version string, not a lockfile, is the source of truth (`dpkg -l`, `rpm -q`, or the binary's own `--version`).

  2. Fix

    Upgrade the affected component to the fixed release for CVE-2020-35730, or apply your distribution's backported patch — distro builds are often patched at an older version number, so check your vendor's advisory rather than the upstream version alone.

  3. Workarounds

    Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

UbuntuMEDIUM
USN-5182-1Ubuntu

Frequently Asked Questions

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.
O3 Security · Impact-Aware SCA

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CVE-2020-35730: roundcubemail XSS (Medium 6.1, KEV)