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 2132 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)
- 32.9% probability of exploitation in the next 30 days, higher than 98.3% 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 2025-10-21
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. Weaponised exploit code for CVE-2020-35730 is publicly available. 2 public proof-of-concept repositories are tracked for this identifier. It currently carries a trending score of 48 in the Threadlinqs vulnerability feed.
- skyllpro/CVE-2021-44026-PoC (github)
- trickest/cve (trickest)
Affected products and versions
- Roundcube: Webmail
- Fedoraproject: Fedora 32, Fedora 33
- Debian: Linux 9.0
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
3 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.
- Russia (GRU Unit 26165 / APT28) Runs Multi-Vector Surveillance, Intimidation, Sabotage and Cyber Espionage Campaign Against Europe's Ukraine Defence Supply Chain — HIGH · 2026-08-16
- Operation RoundPress: TA458 Deploys SpyPress Malware via Half-Click Webmail Zero-Days (CVE-2025-27915, CVE-2025-3929, CVE-2026-8496) — CRITICAL · 2026-07-23
- APT28/UAC-0001 Sustained Cyber Espionage Against Ukraine & EU (2024-2026 New TTPs) — HIGH · 2026-02-12
Sources
Enriched from CVE.org, FIRST EPSS, CISA KEV, public proof-of-concept repositories. Last verified by Threadlinqs on .
Vendor advisory and patch
Other references
Showing 7 of 9 recorded references.