CVE-2021-30116
CVE-2021-30116 is a security flaw in Kaseya Virtual System/Server Administrator (VSA), remote-support software IT providers use to manage their customers’ computers. Attackers can get into Kaseya Virtual System/Server Administrator (VSA) without a valid password. 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, and says ransomware gangs have used it.[1]
Kaseya Virtual System/Server Administrator (VSA) 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. Kaseya has published a fix or advice.
Description
CISA calls it an information disclosure in Kaseya Virtual System/Server Administrator (VSA). In its words: “Kaseya Virtual System/Server Administrator (VSA) contains an information disclosure vulnerability allowing an attacker to obtain the sessionId that can be used to execute further attacks against the system.”[1]
The CVE record adds: “Kaseya VSA before 9.5.7 allows credential disclosure, as exploited in the wild in July 2021. By default Kaseya VSA on premise offers a download page where the clients for the installation can be downloaded. The default URL for this page is https://x.x.x.x/dl.asp When an attacker download a client for Windows and installs it, the file KaseyaD.ini is generated (C:\Program Files (x86)\Kaseya\XXXXXXXXXX\KaseyaD.ini) which contains an Agent_Guid and AgentPassword This Agent_Guid and AgentPassword can be used to log in on dl.asp (https://x.x.x.x/dl.asp?un=840997037507813&pw=113cc622839a4077a84837485ced6b93e440bf66d44057713cb2f95e503a06d9) This request authenticates the client and returns a sessionId cookie that can be used in subsequent attacks to bypass authentication. Security issues discovered --- * Unauthenticated download page leaks credentials * Credentials of agent…”[2]
The underlying weakness is CWE-522, in MITRE’s list of common software weaknesses.
It scores 9.8 out of 10 on the Common Vulnerability Scoring System, which rates it critical, scored by NVD using CVSS 3.1.[2]
Affected versions
NVD’s record doesn’t list version ranges for it; Kaseya’s advisory has them[3]. CISA names the product as Kaseya Virtual System/Server Administrator (VSA).
Most families won’t have Kaseya Virtual System/Server Administrator (VSA); it’s for whoever looks after IT at work.
Exploitation
CISA added it to its catalog of known exploited vulnerabilities on 3 Nov 2021, 117 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 17 Nov 2021 to fix it.[1] CISA says ransomware gangs have used it.
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 86%. That’s in the top 1% of the flaws it scores.[4]
CISA assesses it as automatable: attackers can run it against many targets at once.
CISA doesn’t say who was attacked, or how.
Fix
Kaseya has published a fix or advice.[3] CISA’s required action: “Apply updates per vendor instructions.”[1]
- Check whether you use it.Kaseya Virtual System/Server Administrator (VSA) 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 17 Nov 2021 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 9.8.[2] | |
| CISA adds it to its catalog of flaws known to be used in attacks, noting that ransomware gangs have used it.[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 86%.[4] |
See also
Other Kaseya Virtual System/Server Administrator (VSA) flaws
- CVE-2017-18362: VSA SQL injection ·
- CVE-2018-20753: VSA remote code execution ·
Similar flaws
- CVE-2021-22681, Rockwell products: insufficient protected credentials ·
- CVE-2020-29583, Zyxel products: use of hard-coded credentials ·
- CVE-2017-9248, Progress ASP.NET AJAX and Sitefinity: telerik UI for ASP.NET AJAX and sitefinity cryptographic weakness ·
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 Kaseya flaw on CISA’s list · Everything added in November 2021
References
- ^ Cybersecurity and Infrastructure Security Agency. “Kaseya Virtual System/Server Administrator (VSA) Information Disclosure Vulnerability”. Known Exploited Vulnerabilities Catalog, added 3 Nov 2021.
- ^ National Institute of Standards and Technology. “CVE-2021-30116 Detail”. National Vulnerability Database, published 9 Jul 2021.
- ^ Kaseya. Advisories and fixes: helpdesk.kaseya.com.
- ^ FIRST. “Exploit Prediction Scoring System”. EPSS 0.857, percentile 99.7, 31 Oct 2026.
- CVE Program. “CVE-2021-30116”. 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.