Threats / Roundcube / CVE-2020-35730
CVE-2020-35730
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Roundcube Webmail vulnerability
Roundcube Webmail contains a cross-site scripting vulnerability in linkref_addinindex that allows attackers to inject JavaScript through plain text email messages with malicious link references.
Verdict
Today item — known-exploited.
An attacker can craft a plain text email with JavaScript embedded in a link reference element. When processed by the vulnerable linkref_addinindex function in rcube_string_replacer.php, the script executes in the victim's browser, enabling session hijacking, credential theft, or malware distribution
01
Is it exploitable?
— the evidence, ranked above the scoreExploit available
Public proof-of-concept exploit code is cataloged for this vulnerability.We link the existence of the exploit; we do not host or redistribute payloads.
Reported exploitation
16 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2023-06-22).
Probability (EPSS)
EPSS 0.32365 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Roundcube, Roundcube Webmail. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-79 Cross-site Scripting (XSS) — weakness family: Web / client.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a plain text email containing JavaScript code within a link reference element.
Business
The organization's email infrastructure becomes a vector for client-side attacks against all users who open the message.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I send the malicious email to target users of Roundcube Webmail.
Business
User sessions and credentials are exposed to compromise when the email is rendered in the vulnerable application.
3
Lateral reach — past segmentation narrative 3
Attacker
I execute arbitrary JavaScript in the victim's browser context within the Roundcube application.
Business
Attackers gain unauthorized access to user accounts, email data, and can pivot to internal systems or launch further attacks.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
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