CVE-2023-5631
CVE-2023-5631 is a security flaw in Roundcube Webmail, webmail software many hosting companies and universities run. Attackers can run code in the browser of someone using Roundcube Webmail and act as them. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 26 Oct 2023.[1]
Roundcube Webmail is business software or equipment. Most families won’t have it, but attackers break into it to get inside companies, and from there to what those companies hold about their customers, patients and staff. Fixed in version 1.6.3, 1.5.4 and 1.5.14 of Roundcubemail.
Description
CISA calls it a persistent cross-site scripting (XSS) in Roundcube Webmail. In its words: “Roundcube Webmail contains a persistent cross-site scripting (XSS) vulnerability that allows a remote attacker to run malicious JavaScript code.”[1]
The CVE record adds: “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.”[2]
The underlying weakness is cross-site scripting (CWE-79), in MITRE’s list of common software weaknesses.
It scores 5.4 out of 10 on the Common Vulnerability Scoring System, which rates it medium, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record lists these fixed versions: in each line, everything before the version shown is affected.[2]
| Product | Fixed in |
|---|---|
| Roundcubemail | 1.6.3 |
| Roundcubemail | 1.5.4 |
| Roundcubemail | 1.5.14 |
Most families won’t have Roundcube Webmail; it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 26 Oct 2023, 8 days after it was made public. CISA lists a flaw only when it has reliable evidence of it being exploited, and gave US federal agencies until 16 Nov 2023 to fix it.[1]
FIRST’s Exploit Prediction Scoring System, which estimates how likely a flaw is to be used in attacks in the next 30 days from what it sees across the internet, puts it at 76%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as not automatable: each attack takes some work.
CISA doesn’t say who was attacked, or how.
Fix
Roundcube has published a fix or advice.[3] CISA’s required action: “Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.”[1]
- Check whether you use it.Roundcube Webmail is business software or equipment, so most families won’t have it. If you run a business, or work from home on company equipment, ask whoever looks after your IT.
- Send this page to your IT person.Ask them to confirm it’s fixed (fixed in version 1.6.3, 1.5.4 and 1.5.14 of Roundcubemail), or not in use. CISA gave US government agencies until 16 Nov 2023 to fix it.
- If it can’t be fixed, take it offline.CISA’s advice when there’s no fix is to stop using the product, or take it off the internet, until there is one.
You can’t fix someone else’s server, but you can watch for what follows a break-in like this: a breach notice, a password reset you didn’t ask for, or a scam message that knows things it shouldn’t. HARD watches for those for you and your family.
Timeline
| Date | Event |
|---|---|
| The flaw is made public in the National Vulnerability Database, with a severity score of 5.4.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks.[1] | |
| CISA’s deadline for US government agencies to fix it.[1] | |
| FIRST puts the odds of it being used in attacks in the next 30 days at 76%.[4] |
See also
Other Roundcube Webmail flaws
- CVE-2025-68461: cross-site scripting ·
- CVE-2025-49113: deserialization of untrusted data ·
- CVE-2024-42009: cross-site scripting ·
- CVE-2024-37383: cross-site scripting (XSS) ·
- CVE-2020-13965: cross-site scripting (XSS) ·
- CVE-2023-43770: persistent cross-site scripting (XSS) ·
Other Roundcube flaws
- CVE-2021-44026, Roundcube Webmail: webmail SQL injection ·
- CVE-2020-35730, Roundcube Webmail: webmail cross-site scripting (XSS) ·
- CVE-2020-12641, Roundcube Webmail: webmail remote code execution ·
- CVE-2017-16651, Roundcube Webmail: webmail file disclosure ·
Other cross-site scripting flaws
- CVE-2026-42897, Microsoft: exchange server cross-site scripting ·
- CVE-2025-48700, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
- CVE-2025-66376, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
- CVE-2021-26829, OpenPLC ScadaBR: cross-site scripting ·
- CVE-2025-27915, Synacor Zimbra Collaboration Suite (ZCS): cross-site scripting ·
Every Roundcube flaw on CISA’s list · Everything added in October 2023
References
- ^ Cybersecurity and Infrastructure Security Agency. “Roundcube Webmail Persistent Cross-Site Scripting (XSS) Vulnerability”. Known Exploited Vulnerabilities Catalog, added 26 Oct 2023.
- ^ National Institute of Standards and Technology. “CVE-2023-5631 Detail”. National Vulnerability Database, published 18 Oct 2023.
- ^ Roundcube. Advisories and fixes: roundcube.net, roundcube.net, bugs.debian.org.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.763, percentile 99.5, 31 Oct 2026.
- CVE Program. “CVE-2023-5631”. The official CVE record.
This article is built from CISA’s catalog (version 2026.10.30), NVD’s record and FIRST’s scores, kept in HARD’s database and checked every morning. The plain English is HARD’s.