Threat Intelligence / CVE / CVE-2020-35730

CVE-2020-35730 — Roundcube Webmail

CISA KEV
CVSS v3.1 6.1 (MEDIUM) · EPSS 64.8% (higher than 98.4% of all scored CVEs) · Priority 9/10 · Published 2020-12-28

As of 2025-11-04, CVE-2020-35730 is a MEDIUM-severity vulnerability in Roundcube Webmail, CVSS v3.1 6.1, EPSS 64.8% (98.4th percentile). It is listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-22), with a US federal remediation deadline of 2023-07-13. Threadlinqs Intelligence links 2 tracked threat campaigns to CVE-2020-35730, most recently “Russia (GRU Unit 26165 / APT28) Runs Multi-Vector Surveillance, Intimidation, Sabotage and Cyber Espionage Campaign Against Europe's Ukraine Defence Supply Chain”.

Last updated: 2025-11-04

What is 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.

The record classifies CVE-2020-35730 under weakness class CWE-79. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first. 4 affected-product entries are recorded, across 3 vendors, listed below. The identifier was first published 2085 days ago.

Severity and exploitation probability

CVSS v3.1 base score
6.1 — MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
EPSS (FIRST)
64.8% probability of exploitation in the next 30 days, higher than 98.4% of all scored CVEs
CISA KEV
Listed since 2023-06-22, federal remediation deadline 2023-07-13
Threadlinqs priority
9/10 — CISA KEV-listed, which Threadlinqs floors at 9
Published
2020-12-28, last modified 2025-11-04

Is CVE-2020-35730 being exploited?

CISA added CVE-2020-35730 to the Known Exploited Vulnerabilities catalog on 2023-06-22, which means the agency holds evidence of exploitation in the wild; US federal civilian agencies had to remediate it by 2023-07-13 under BOD 22-01. It currently carries a trending score of 40 in the Threadlinqs vulnerability feed.

Affected products and versions

How to fix CVE-2020-35730

The record marks a vendor fix as available for CVE-2020-35730. Patch reference: https://github.com/roundcube/roundcubemail/compare/1.4.9...1.4.10. Vendor advisory: https://github.com/roundcube/roundcubemail/compare/1.4.9...1.4.10. Because CVE-2020-35730 is KEV-listed, US federal civilian agencies were required to apply the vendor fix, or stop using the product, by 2023-07-13. Apply the vendor fix referenced above to every affected product listed in this record, then confirm the running version against the vendor advisory.

Threat activity tracking CVE-2020-35730

2 tracked threats in the Threadlinqs corpus reference CVE-2020-35730, either in the campaign’s CVE list or as an indicator on the campaign record.

Sources

Seeded from nvd and not yet processed by the Threadlinqs enrichment pipeline, so blank CVSS, EPSS or KEV fields above mean NOT MEASURED rather than measured-absent.

Full detection coverage & IOCs for threats exploiting CVE-2020-35730 are available via the Threadlinqs MCP server (Purple tier). View plans →

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