Security readout for executives and security teams
Plain-English summary
Roundcube Webmail versions before 1.2.13, 1.3.16, and 1.4.10 mishandle JavaScript placed in a link reference inside a plain text email. If a user interacts with the crafted message, attacker-controlled script can run in the webmail session. CISA KEV listing raises urgency despite medium CVSS.
Executive priority
Treat as urgent for any exposed Roundcube deployment. The technical impact is limited to script execution in a user’s webmail context, but known exploitation means remediation should be handled ahead of routine medium-severity backlog work.
Technical view
CVE-2020-35730 is a stored/reflected XSS-style issue in Roundcube’s link reference processing, specifically linkref_addindex in rcube_string_replacer.php. The CVSS 3.1 score is 6.1: network reachable, low complexity, no privileges, user interaction required, changed scope, low confidentiality and integrity impact, no availability impact.
Likely exposure
Exposure is most likely where Roundcube Webmail is deployed on vulnerable branches: before 1.2.13, 1.3.x before 1.3.16, or 1.4.x before 1.4.10. Internet-facing webmail used by staff, customers, or administrators should be prioritized.
Exploitation context
The source bundle states an attacker can send a plain text email containing JavaScript in a link reference element. User interaction is required. CISA KEV indicates known exploitation, but the supplied sources do not provide campaign details, exploitation volume, or target sectors.
Researcher notes
The evidence identifies vulnerable Roundcube version ranges, the affected PHP component, and the malicious email condition. It does not provide enough detail to assess exploit reliability, bypasses, or real-world attacker procedures beyond the KEV signal.
Mitigation direction
- Upgrade Roundcube to 1.2.13, 1.3.16, 1.4.10, or a later supported release.
- Use vendor or distribution packages that explicitly include the CVE-2020-35730 fix.
- Prioritize internet-facing Roundcube systems and mailboxes used by privileged staff.
- Review Roundcube, Debian, Fedora, and local vendor guidance before relying on package names alone.
- Until patched, warn users against interacting with suspicious links in webmail messages.
Validation and detection
- Inventory all Roundcube Webmail instances and record their exact versions.
- Confirm deployed versions are fixed or include backported CVE-2020-35730 patches.
- Check package changelogs or vendor advisories for explicit CVE coverage.
- Review webmail access logs for unusual sessions after suspicious emails.
- Track remediation against the CISA KEV listing because exploitation is documented.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-79: User-session and phishing behavior lookup
Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2020-35730 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Medium
- CVSS
- 6.1 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N2.82.7Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
6.1MediumVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://roundcube.net/download/CVE reference · x_refsource_MISC
- https://github.com/roundcube/roundcubemail/compare/1.4.9...1.4.10CVE reference · x_refsource_CONFIRM
- https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=978491CVE reference · x_refsource_CONFIRM
- https://www.alexbirnberg.com/roundcube-xss.htmlCVE reference · x_refsource_MISC
- https://github.com/roundcube/roundcubemail/releases/tag/1.4.10CVE reference · x_refsource_CONFIRM
- https://github.com/roundcube/roundcubemail/releases/tag/1.3.16CVE reference · x_refsource_CONFIRM
- https://github.com/roundcube/roundcubemail/releases/tag/1.2.13CVE reference · x_refsource_CONFIRM
- FEDORA-2021-2cb0643316CVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-73359af51cCVE reference · vendor-advisory, x_refsource_FEDORA
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2020-35730CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.