VulnerabilityPublished 18 Oct 2023Updated 21 Oct 2025

CVE-2023-5631: Roundcube Roundcubemail · Cross-site Scripting

Affects Roundcube RoundcubemailSource CVE Database V5

Exploited in the wild · KEV due 16 Nov 2023 · 76% EPSS · fixed in 1.6.4 : patch Roundcube Roundcubemail now.

Data as of 26 Oct 2026, 17:16 UTC

CVSS 3.1 base score

6.1Medium

How severe the flaw is on the 0–10 CVSS scale.

KEV deadline: 16 Nov 2023 US federal agencies must patch by this date; a sensible deadline for everyone else. Other KEV due dates
EPSS: 76.9% chance of exploitation in 30 days – higher than 99% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.6.4, 1.5.5, 1.4.15

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: Required
Scope: Changed
Confidentiality: Low
Integrity: Low
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

t = 0 is the CVE’s publication on cve.org

Disclosed: evidence found.
CVE published 18 Oct 2023
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: evidence found.
Listed in CISA KEV 8 days after disclosure
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

CVE ID reserved
by ESET, spol. s r.o.
18 Oct 202306:50 UTC, 8 hours before disclosure
CVE published
on cve.org
18 Oct 202314:51 UTC, t = 0
Added to CISA KEV (opens in a new tab)
exploitation confirmed
26 Oct 2023, 8 days after disclosure
KEV remediation due
US federal deadline
16 Nov 2023, 29 days after disclosure

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CISA KEV (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade roundcube/roundcubemail to 1.6.4, 1.5.5 or 1.4.15.

Affected software

Product	Affected	Fixed in
GitHubroundcube/roundcubemail`pkg:github/roundcube/roundcubemail`Other threats	Affected <1.4.15 >=1.5.0 <1.5.5 >=1.6.0 <1.6.4 =1.5.0 =1.6.0	Fixed in 1.4.15 1.5.5 1.6.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

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.

Impact

For European organizations, the exploitation of CVE-2023-5631 could lead to unauthorized access to sensitive email content, session hijacking, and potential lateral movement within internal networks if attackers leverage stolen credentials or session tokens. Given that Roundcube is a popular open-source webmail client used by many institutions, including governmental, educational, and private sectors across Europe, the risk of data leakage and compromise of confidential communications is significant. Attackers could use this vulnerability to implant persistent malicious scripts, potentially leading to phishing campaigns, credential theft, or further exploitation of internal systems. The impact is heightened in environments where webmail is a critical communication tool and where users may not be trained to recognize malicious emails. Additionally, the scope change indicated in the CVSS vector suggests that the vulnerability could affect other components or services integrated with Roundcube, amplifying the potential damage. Disruption of email services or loss of trust in communication channels could also have operational and reputational consequences for affected organizations.

Mitigation

1. Immediately upgrade Roundcube installations to versions 1.4.15, 1.5.5, or 1.6.4 or later, where the vulnerability has been patched. 2. If upgrading is not immediately feasible, disable SVG rendering in emails by configuring Roundcube to strip or block SVG content or by disabling HTML email rendering temporarily. 3. Implement strict Content Security Policy (CSP) headers to restrict the execution of inline scripts and limit the domains from which scripts can be loaded. 4. Educate users to be cautious when opening emails from unknown or untrusted sources, especially those containing HTML or SVG content. 5. Monitor webmail logs for unusual activity that could indicate exploitation attempts, such as repeated access to crafted emails or anomalous session behaviors. 6. Employ web application firewalls (WAFs) with rules targeting XSS payloads in HTTP requests and responses related to Roundcube. 7. Regularly audit and sanitize email content at the mail server level to detect and block malicious payloads before delivery to end users. 8. Review and harden the overall email infrastructure, including spam filtering and anti-malware scanning, to reduce the likelihood of malicious emails reaching users.

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #1OWASP Top 10 A05:2025: Injection (opens in a new tab)
The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Implementation · Architecture and Design
Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages.
Architecture and Design · Implementation · Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide…
OWASP Cheat Sheets
Cross Site Scripting Prevention (opens in a new tab)
DOM based XSS Prevention (opens in a new tab)
Injection Prevention (opens in a new tab)
Abuse Case (opens in a new tab)
Deserialization (opens in a new tab)
OWASP ASVS 4.0.3
V5.3.3 (opens in a new tab)
V1.5.1 (opens in a new tab)
Attack patterns
XSS Using MIME Type Mismatch (opens in a new tab)
DOM-Based XSS (opens in a new tab)
Reflected XSS (opens in a new tab)
Stored XSS (opens in a new tab)
Cross-Site Scripting (XSS) (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

Timeline

What to do

Affected software

Description

AI analysisMachine-generated, updated 21 Oct 2025, 20:01 UTC

WeaknessesCWE-79

Technical details

References

Community reviews

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