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Fencer Vulns
critical 10.0

CVE-2021-30116 kev+ ransomware in the critical feed json

Unauthenticated credential leak and business logic flaw in Kaseya VSA <= v9.5.6

published 2021-07-09 5 y ago modified 2026-08-14 2 mo ago also EUVD-2021-17056

cvss
10.0
version 3.1, CNA
cisa kev
Exploited
added 2021-11-03, used in ransomware
epss
85.7%
EPSS 85.7% chance of exploitation in 30 days, percentile 99.7%
public exploits
0
none known, plus a Nuclei check

Summary

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 software can be used to obtain a sessionId (cookie) that can be used for services not intended for use by agents * dl.asp accepts credentials via a GET request * Access to KaseyaD.ini gives an attacker access to sufficient information to penetrate the Kaseya installation and its clients. Impact --- Via the page /dl.asp enough information can be obtained to give an attacker a sessionId that can be used to execute further (semi-authenticated) attacks against the system.

Patch / fix

cisa required action Apply updates per vendor instructions.

  • kaseya vsa_agent 9.5.0.24
  • kaseya vsa_server 9.5.7a

Timeline

  1. CISA SSVC: exploitation active
  2. Published
  3. Added to CISA KEV
  4. CISA patch deadline

Known exploited

Added
5 y ago
Patch by
2021-11-17 (4 y ago)
Ransomware
Known to be used in ransomware campaigns
Required action
Apply updates per vendor instructions.
Vendor, product
Kaseya, Virtual System/Server Administrator (VSA)
CISA name
Kaseya Virtual System/Server Administrator (VSA) Information Disclosure Vulnerability

Ransomware

Groups reported to have exploited it in intrusions.

  • REvil ransomware gang

reported by tenable.com

Ransomware Vulnerability Matrix by BushidoUK (github.com/BushidoUK/Ransomware-Vulnerability-Matrix), reformatted per CVE. CC BY 4.0

CISA SSVC

Exploitation
Active, exploited in the wild
Automatable
yes
Technical impact
total
Assessed
5 y ago

Exploit prediction

85.73% chance of exploitation in the next 30 days, higher than 99.7% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • Nuclei template Kaseya VSA < 9.5.7 - Credential Disclosure via Windows Agent nuclei detection template
  • secpod.com https://www.secpod.com/blog/kaseya-vsa-zero-day-by-revil/ referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 10.0 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 7.5 AV:N/AC:L/Au:N/C:P/I:P/A:P

Classification

Weakness
  • CWE-522 Insufficiently Protected Credentials

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.