CVE-2017-16651
CVE-2017-16651 is a security flaw in Roundcube Webmail, webmail software many hosting companies and universities run. Attackers are using a flaw in Roundcube Webmail. The US Cybersecurity and Infrastructure Security Agency (CISA) added it to its catalog of flaws known to be used in attacks on 3 Nov 2021.[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. Roundcube has published a fix or advice.
Description
CISA calls it a webmail file disclosure in Roundcube Roundcube Webmail. In its words: “Roundcube Webmail contains a file disclosure vulnerability caused by insufficient input validation in conjunction with file-based attachment plugins, which are used by default.”[1]
The CVE record adds: “Roundcube Webmail before 1.1.10, 1.2.x before 1.2.7, and 1.3.x before 1.3.3 allows unauthorized access to arbitrary files on the host's filesystem, including configuration files, as exploited in the wild in November 2017. The attacker must be able to authenticate at the target system with a valid username/password as the attack requires an active session. The issue is related to file-based attachment plugins and _task=settings&_action=upload-display&_from=timezone requests.”[2]
The underlying weakness is CWE-552, in MITRE’s list of common software weaknesses.
It scores 7.8 out of 10 on the Common Vulnerability Scoring System, which rates it high, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Roundcube’s advisory has them[3]. CISA names the product as Roundcube Roundcube Webmail.
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 3 Nov 2021, 1,455 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 3 May 2022 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 46%. That’s in the top 2% 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 updates per vendor instructions.”[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, or not in use. CISA gave US government agencies until 3 May 2022 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 7.8.[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 46%.[4] |
See also
Other Roundcube Webmail flaws
- CVE-2021-44026: webmail SQL injection ·
- CVE-2020-35730: webmail cross-site scripting (XSS) ·
- CVE-2020-12641: webmail remote code execution ·
Other Roundcube flaws
- CVE-2025-68461, Roundcube Webmail: cross-site scripting ·
- CVE-2025-49113, Roundcube Webmail: deserialization of untrusted data ·
- CVE-2024-42009, Roundcube Webmail: cross-site scripting ·
- CVE-2024-37383, Roundcube Webmail: cross-site scripting (XSS) ·
- CVE-2020-13965, Roundcube Webmail: cross-site scripting (XSS) ·
Similar flaws
- CVE-2026-21589, Atlassian products: files or directories accessible to external parties ·
- CVE-2025-11371, Gladinet CentreStack and Triofox: files or directories accessible to external parties ·
- CVE-2020-17519, Apache Flink: improper access control ·
Added the same day
- CVE-2021-42258, BQE BillQuick Web Suite: SQL injection ·
- CVE-2021-42013, Apache HTTP Server: path traversal ·
- CVE-2021-41773, Apache HTTP Server: path traversal ·
- CVE-2021-40539, Zoho ManageEngine: aDSelfService plus authentication bypass ·
- CVE-2021-40444, Microsoft MSHTML: remote code execution ·
Every Roundcube flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Roundcube Webmail File Disclosure Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2017-16651 Detail”. National Vulnerability Database, published 9 Nov 2017.
- ^ Roundcube. Advisories and fixes: roundcube.net.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.457, percentile 98.8, 31 Oct 2026.
- CVE Program. “CVE-2017-16651”. 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.