Roundcube Webmail Persistent Cross-Site Scripting (XSS) Vulnerability
Roundcube · Webmail
Roundcube Webmail (Roundcube before 1.4.15, 1.5.x before 1.5.5, and 1.6.x before 1.6.4) contains a stored cross-site scripting flaw in the HTML sanitisation logic of program/lib/Roundcube/rcube_washtml.php, which mishandles crafted SVG content embedded in HTML e-mail. A remote attacker can exploit this by sending a malicious HTML e-mail containing a crafted SVG document that causes arbitrary JavaScript to execute, requiring the victim to interact with the message (for example, by opening it) and low-privileged access to the application.
Roundcube before 1.4.15, 1.5.x before 1.5.5, and 1.6.x before 1.6.4 allows stored XSS via an HTML e-mail message with a crafted SVG document because of program/lib/Roundcube/rcube_washtml.php behavior. This could allow a remote attacker to load arbitrary JavaScript code.
- Exploited
- Yes, in CISA KEV
- Reports
- 0
- Tactics
- 2/15
How an attack unfolds
Based on MITRE ATT&CKA public catalogue of the techniques attackers use, maintained by MITRE. Patchfirst uses it to describe what attackers do with a vulnerability. mappings. Select a step to see the evidence.Exploitation timelineDated milestones for a CVE: when it was disclosed, when exploit code became public, when exploitation was confirmed, and when threat reports named it.
First seen exploited 7 days after disclosure.
- Disclosedday 0
- First seen exploitedVulnCheck KEV evidence+7 days
- Added to CISA KEVEU database agrees+8 days
CISA KEV listing is when exploitation was confirmed, not necessarily the first attack.
MITRE ATT&CKA public catalogue of the techniques attackers use, maintained by MITRE. Patchfirst uses it to describe what attackers do with a vulnerability. techniques
3 TechniqueOne specific attacker behaviour in MITRE ATT&CK, such as T1190 “Exploit Public-Facing Application”. IDs with a dot, like T1059.004, are sub-techniques., grouped by TacticThe attacker’s goal at a stage of an attack in MITRE ATT&CK, such as Initial Access or Persistence. Each technique belongs to one or more tactics. in kill-chain order 3ExecutionTA0002
This vulnerability is exploited by an adversary via a malicious e-mail containing a crafted SVG document. When a user views the e-mail, the remote attacker can load arbitrary JavaScript code on the victim's machine. In recent campaign Winter Vivern group exploited this vulnerability. The attack chains typically start with a phishing mail sent containing a Base64-encoded payload embedded in the HTML source code. The payload gets decoded and injects a remote javascript, checkupdate.js, in current user session. The checkupdate.js script serves as a loader, enabling the execution of a final JavaScript payload which is designed to exfiltrate email messages. The attackers weaponized this XSS flaw to carry out their malicious activities, ultimately allowing them to harvest email messages from their victims' accounts to a C2 server. The attack chain requires minimal user interaction, the attack gets executed only in viewing the malicious email in a web browser.
ExfiltrationTA0010
Detection
0 rules for this CVE · 38 general rules for its techniquesRules for this CVE
0Sigma ruleAn open, vendor-neutral detection rule for log data. Security teams convert Sigma rules into searches for their own SIEM. that reference CVE-2023-5631 directly.CVE-specific rules are not available in this build. Search SigmaHQ ↗
General rules for this CVE’s techniques
These detect the technique in general, not this specific vulnerability.
Malicious LinkT1204.0014 general rules
- Symlink Etc Passwdhightest
- Potential ClickFix Execution Pattern - Registryhighexperimental
- Suspicious ClickFix/FileFix Execution Patternhighexperimental
- Suspicious Execution via macOS Script Editormediumtest
JavaScriptT1059.00729 general rules
- Adwind RAT / JRAThightest
- Adwind RAT / JRAT File Artifacthightest
- Csc.EXE Execution Form Potentially Suspicious Parenthightest
- Cscript/Wscript Uncommon Script Extension Executionhightest
- HackTool - CACTUSTORCH Remote Thread Creationhightest
- HackTool - Koadic Executionhightest
- HTML Help HH.EXE Suspicious Child Processhightest
- JXA In-memory Execution Via OSAScripthightest
Exfiltration Over C2 ChannelT10415 general rules
- Equation Group C2 Communicationhightest
- OpenCanary - TFTP Requesthightest
- Shai-Hulud NPM Package Malicious Exfiltration via Curlhighexperimental
- Network Communication Initiated To Portmap.IO Domainmediumtest
- Tunneling Tool Executionmediumtest
Sigma rules © SigmaHQ, Detection Rule License 1.1; linked, not reproduced.
What security researchers reported
Not named in any threat report yetAlso mentioned in 50 community threat pulses (AlienVault OTX)
Weaker evidencePulses are indicator collections that anyone can publish. A mention is not confirmation of exploitation.
- Actively_Exploited_Kev | Oct 30, 202629 Oct 2026
- Actively_Exploited_Kev | Oct 29, 202628 Oct 2026
- Actively_Exploited_Kev | Oct 28, 202627 Oct 2026
- Actively_Exploited_Kev | Oct 27, 202626 Oct 2026
- Actively_Exploited_Kev | Oct 24, 202623 Oct 2026
- Actively_Exploited_Kev | Oct 23, 202622 Oct 2026
- 44 more on OTX