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Actively exploited

CVE-2020-35730 Roundcube Webmail Cross-Site Scripting (XSS) Vulnerability

Roundcube Webmail contains a cross-site scripting (XSS) vulnerability that allows an attacker to send a plain text e-mail message with Javascript in a link reference element that is mishandled by linkref_addinindex in rcube_string_replacer.php.

From the CISA KEV catalogue version 2026.11.06, with Cybergen analysis. Updated 6 Nov 2026.

Our Assessment

Should You Worry?

Patch nowCybergen assessment
  • CISA confirmed exploitation in the wild and added it to the Known Exploited Vulnerabilities catalogue on 22 Jun 2023.
  • Rated Medium severity (CVSS 6.1, scored by CISA).
  • This product type is often exposed to the internet, which is where attackers scan for it first.
  • It has been in the catalogue for 1,233 days. Systems still unpatched now have almost certainly been scanned for it.
The Vulnerability

What It Is

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.

From Watch to Action

What To Do Now

  1. 1

    Find it

    Search your asset inventory and external attack surface for Roundcube Webmail. Include cloud images, appliances and anything a supplier runs for you.

    Attack Surface Management
  2. 2

    Fix it

    Apply updates per vendor instructions.

    Vulnerability Management
  3. 3

    Hunt for compromise

    If an affected system was reachable before you patched, assume it may have been hit. Check logs, new accounts, web shells and outbound connections from the date of exposure.

    Incident Response
  4. 4

    Prove it is fixed

    Rescan or test the system after patching. Upgrades that fail silently and forgotten secondary instances are common.

    Penetration Testing

Vendor Advisories

Regulation

The Compliance Clock

Cyber EssentialsCyber Essentials requires high and critical updates (CVSS 7.0 or above) within 14 days of release. Treat any exploited flaw the same way.NIS2If exploitation causes a significant incident, essential and important entities owe their CSIRT an early warning within 24 hours and a notification within 72 hours.DORAFinancial entities must classify ICT incidents and send an initial notification for a major incident within strict deadlines, with exploited flaws a common cause.US federal (BOD 22-01)Federal civilian agencies had until 13 Jul 2023 to remediate. A sensible benchmark for everyone else.

General guidance, not legal advice. Your obligations depend on your sector, scope and jurisdiction.

Stay Ahead

More Exploited Roundcube Flaws

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CVE-2025-49113RoundCube Webmail Deserialization of Untrusted Data VulnerabilityAdded 20 Feb 2026CVE-2025-68461RoundCube Webmail Cross-site Scripting VulnerabilityAdded 20 Feb 2026CVE-2024-42009RoundCube Webmail Cross-Site Scripting VulnerabilityAdded 9 Jun 2025CVE-2024-37383RoundCube Webmail Cross-Site Scripting (XSS) VulnerabilityAdded 24 Oct 2024CVE-2020-13965Roundcube Webmail Cross-Site Scripting (XSS) VulnerabilityAdded 26 Jun 2024CVE-2023-43770Roundcube Webmail Persistent Cross-Site Scripting (XSS) VulnerabilityAdded 12 Feb 2024

All 11 exploited Roundcube vulnerabilities

Not Sure If You Are Exposed?

Our attack surface and vulnerability teams can check your internet-facing estate for CVE-2020-35730 and every other exploited flaw on the list.

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Evidence

Sources

  1. CISA Known Exploited Vulnerabilities catalogue
  2. NVD: CVE-2020-35730
  3. CVE record: CVE-2020-35730
  4. FIRST EPSS
  5. roundcube.net/news/2020/12/27/security-updates-1.4.10-1.3.16-and-1.2.13
  6. roundcube.net/download/
  7. github.com/roundcube/roundcubemail/compare/1.4.9...1.4.10
  8. bugs.debian.org/cgi-bin/bugreport.cgi?bug=978491
  9. alexbirnberg.com/roundcube-xss.html
  10. github.com/roundcube/roundcubemail/releases/tag/1.4.10
  11. github.com/roundcube/roundcubemail/releases/tag/1.3.16
  12. github.com/roundcube/roundcubemail/releases/tag/1.2.13