CriticalCVE-2021-30116

    Unauthenticated credential leak and business logic flaw in Kaseya VSA <= v9.5.6 (CVE-2021-30116)

    Published In CISA KEV since Sources: CVE.org

    What is affected, what to do

    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.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update Kaseya Vsa Agent to version 9.5.0.24, Kaseya Vsa Server to version 9.5.7a. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • Kaseya Vsa Agent lt *..9.5.0.24
    • Kaseya Vsa Server lt *..9.5.7a
    Fixed in
    • Kaseya Vsa Agent 9.5.0.24
    • Kaseya Vsa Server 9.5.7a

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    10.0

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    10.0

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: CVE.org

    85.7 %

    EPSS score

    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.

    Source: FIRST EPSS, percentile 99.72

    Show all metrics
    Severity
    Critical
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    254.55 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    actively exploited
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    10.0 Methodology
    CVSS v3

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    10.0
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

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    85.7 %
    High — model estimates ≥ 50% chance of real-world exploitation within 30 days.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    99.72
    Critical — this CVE ranks in the top fifth of all CVEs scored today (rank ≥ 80%).
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    Actively exploited
    Published
    In CISA KEV since

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    CISA assessment (SSVC)
    Exploitation: active · automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 6 July 2021
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-522

    Response and mitigation

    Why act now?

    Prioritisation rationale

    The flaw is network-reachable without authentication and is the entry point to a chain ending in full control of the VSA server — and therefore every endpoint it manages, the textbook supply-chain lever via managed service providers. CISA flags known ransomware use, and its exploitation likelihood is among the highest of any CVE. Typical targets are MSPs and IT departments running internet-exposed on-prem VSA, with their customers inheriting the risk directly. Any VSA server still running unpatched or publicly reachable should be treated as critical with immediate action; organisations that are merely MSP customers should actively ask their provider for patch status.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Check exposure and pull the VSA web interface off the internet: Put on-prem VSA servers behind VPN or a zero-trust gateway now. https://<vsa>/dl.asp in particular must not be publicly reachable. Until patch status is verified, an offline server beats an exposed one.
      • Upgrade to a fixed release: The CVE description states versions before 9.5.7 are affected; the product list also references vsa_server 9.5.7a. Patch available from the vendor — look up the exact fixed version in the Kaseya advisory rather than assuming 9.5.7 is sufficient.
      • Compromise assessment before bringing it back: Search VSA server IIS logs for GET /dl.asp?un=...&pw=... from unknown source IPs, going back as far as retention allows. Any hit → escalate per your IR plan and check NIS2 reporting deadlines (24 h early warning).
      • Treat agent credentials as burned: Every KaseyaD.ini credential pair (Agent_Guid/AgentPassword) is considered disclosed if dl.asp was reachable. Re-register agents or rotate agent passwords after upgrading; also rotate VSA admin accounts and any domain/service credentials stored in VSA.
      • Protect managed endpoints: VSA can run code on every managed client, so watch agent process activity and, if compromise is suspected, block outbound agent traffic (typically TCP 5721) until resolved.
      • Verify offline backups: Given known ransomware use, confirm backup integrity and isolation immediately.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place the VSA server in a dedicated management zone; allow inbound agent check-in (TCP 5721) only from known client networks/sites, and the web UI (TCP 443) only from the admin VLAN or VPN.
      • WAF/reverse-proxy rule: Block requests to /dl.asp carrying un= or pw= query parameters (e.g. ModSecurity: SecRule REQUEST_URI "@rx (?i)/dl\.asp\?.*(un|pw)=" "id:1030116,deny,status:403,log"). Restrict the agent installer download page to internal networks altogether.
      • IPS signature: Suricata rule on HTTP URI /dl.asp with pw= followed by 64 hex characters (pcre:"/pw=[0-9a-f]{64}/i"), alert or drop.
      • Endpoint hardening: Enforce AV tamper protection on managed clients so the agent context cannot disable it (e.g. via Set-MpPreference); enable ASR rules for process creation from management tooling in audit mode.
      • Least privilege: Review ACLs on C:\Program Files (x86)\Kaseya\; KaseyaD.ini readable only by SYSTEM/Administrators. Apply least-privilege VSA roles and enforce MFA for all console accounts.

    3. Runbook step 3

      Detection rules

      • IIS access log (VSA server): Catch GET-based credential logins. SPL: index=iis cs_uri_stem="/dl.asp" cs_uri_query="*pw=*" | stats count by c_ip, cs_uri_query — any external source IP is suspicious.
      • Session abuse: After a successful dl.asp login, correlate follow-on requests from the same source IP to non-agent endpoints (admin/reporting ASP pages, upload functions) — agent sessions have no business there.
      • Sysmon EID 1 / EDR process ancestry on endpoints: AgentMon.exe → cmd.exe/powershell.exe running certutil -decode, Set-MpPreference, or dropping files into the Kaseya working directory. Sigma shape: ParentImage|endswith: '\AgentMon.exe' AND CommandLine|contains: ['certutil', 'Set-MpPreference', 'DisableRealtimeMonitoring'].
      • Windows events: Defender event 5001 (real-time protection disabled) or 5007 (configuration change) on many hosts at once → likely mass deployment via VSA.
      • Network telemetry (Zeek http.log): uri starting with /dl.asp and containing pw=; also spikes in agent task execution outside maintenance windows.

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    Actively exploited: treat the vulnerability as a priority in vulnerability handling under Art. 21(2)(e) NIS2. If it is exploited in your environment, check the reporting obligation under Art. 23 (early warning within 24 hours).
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    Since 11.09.2026, manufacturers of affected products with digital elements must report actively exploited vulnerabilities under Art. 14 CRA, with an early warning within 24 hours via ENISA's single reporting platform.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: CISA KEV Catalog, cvelistv5, NVD (NIST), CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    kaseyavsa_agent
    • < 9.5.0.24
    • 9.5.0.24
    kaseyavsa_server
    • < 9.5.7a
    • 9.5.7a

    Vendors and products

    Weakness classes (CWE)

    • CWE-522Insufficiently Protected Credentials

      Class

      The product transmits or stores authentication credentials, but it uses an insecure method that is susceptible to unauthorized interception and/or retrieval.

      Entry at MITRE CWE-522

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    CISA KEV CatalogCISA Known Exploited Vulnerability (opens in a new tab)cisa.govactively exploited

    References & sources

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