CVE Intelligence
CISA KEV Medium Cross-site scripting

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

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.

Published Dec 28, 2020 · Updated Oct 13, 2026 · Sources: CISA Known Exploited Vulnerabilities, NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: mitre

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

CISA KEV · Jun 22, 2023 Proofs of concept on GitHub · 1
How the score was calculated
  • Confirmed exploitation (CISA KEV)+35
  • Public exploit/PoC (github)+6
  • EPSS 32.9% (30-day exploitation probability)+15
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Confirmed
CISA KEV, listed Jun 22, 2023
EPSS FIRST
32.92%
ahead of 98% of scored CVEs · Oct 14, 2026
Affects
Debian
Debian Linux and 2 more
CVSS base
6.1
Medium · 4 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
Active
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — github.com (NIST National Vulnerability Database)

CISA required action CISA

Apply updates per vendor instructions.

US federal deadline: Jul 13, 2023 — passed 1190 day(s) ago

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Fedoraproject Fedora, Roundcube Webmail).
  2. Treat as emergency remediation: the CVE is in CISA KEV (confirmed exploitation).
  3. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  4. Apply the fixed version or the patch documented under Remediation.
  5. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
  6. EPSS ahead of 98% of scored CVEs: prioritize it in the patch queue.
  7. Search available logs for exploit probes matching the vulnerability class (cross-site scripting), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Debian Debian Linux version 9.0 Vulnerable NIST National Vulnerability Database
Fedoraproject Fedora version 32version 33 Vulnerable NIST National Vulnerability Database
Roundcube Webmail < 1.2.13≥ 1.3.0 and < 1.3.16≥ 1.4 and < 1.4.10 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
6.1 CVSS 3.1 Medium 2.8 2.7 nvd@nist.gov via NIST National Vulnerability Database
6.1 CVSS 3.1 Medium 2.8 2.7 134c704f-9b21-4f2e-91b3-4a467353bcc0 via NIST National Vulnerability Database
6.1 CVSS 3.1 Medium — — GitHub, Inc. via GitHub Security Advisories
6.1 CVSS 3.1 Medium — — CISA-ADP via CVE Program (cve.org) e CISA ADP
4.3 CVSS 2.0 Medium 8.6 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-79 · Cross-site Scripting (XSS)

Other CVEs with this weakness →

CISA KEV details CISA

CISA lists a CVE once it has evidence of exploitation against real targets.

Listed
Jun 22, 2023
Federal deadline
Jul 13, 2023
passed 1190 day(s) ago
Ransomware use
Unknown

CISA records ransomware use only for campaigns it has confirmed, so “Unknown” means unrecorded, not ruled out. The deadline binds US federal agencies; for everyone else it is a reference date.

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Proofs of concept on GitHub

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 12, 2026 → Oct 14, 2026 · 3 reading(s) · max 32.92%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Monitor CSP violation reports and script payloads in reflected parameters.
  • Hunt retroactively in logs from before Jun 22, 2023 (KEV listing): exploitation may have started earlier.
web/proxy/WAF logsnetwork IDS/IPSapplication logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • Affected products added · roundcube/webmail, fedoraproject/fedora, debian/debian linux
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 6.1
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Added to CISA KEV (detected)
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • Record created in this database
    Oct 13, 2026 · CISA Known Exploited Vulnerabilities
  • 2023
  • Added to CISA KEV catalog
    Jun 21, 2023 · CISA
  • 2020
  • CVE published
    Dec 28, 2020 · mitre

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 13, 2026 – Oct 13, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

17 on the record

Elsewhere on this site

Debian
every CVE for this vendor
2023-06
what else CISA listed that month
Cross-site scripting
same class
CWE-79
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-75010 Incorrect Resource Transfer Between Spheres in Roundcube Webmail Aug 17, 2026
  • CVE-2026-75004 Command Injection in Roundcube Webmail Aug 17, 2026
  • CVE-2026-75006 Server-Side Request Forgery (SSRF) in Roundcube Webmail Aug 17, 2026
  • CVE-2026-75007 Command Injection in Roundcube Webmail Aug 17, 2026
  • CVE-2026-74997 OS Command Injection in Roundcube Webmail Aug 17, 2026
  • CVE-2026-74999 Cross-site Scripting (XSS) in Roundcube Webmail Aug 17, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2020-35730 is "Roundcube Webmail Cross-Site Scripting (XSS) Vulnerability", rated Medium. It affects Debian Linux (Debian); versions are in the scope table. It is in CISA KEV: there is evidence of real-world exploitation. CVSS 6.1 describes technical severity. EPSS 32.92% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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