CriticalCVE-2021-20021

    SonicWall Email Security Improper Privilege Management Vulnerability (CVE-2021-20021)

    Published In CISA KEV since Sources: SingCERT, CVE.org

    What is affected, what to do

    A vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.

    The vulnerability is being actively exploited; treat it as a priority. CISA lists it as used in ransomware campaigns. Update email_security to version 10.0.9.6103, email_security_virtual_appliance to version 10.0.9.6105, hosted_email_security to version 10.0.9.6103. Immediate actions, mitigation and detection rules are in the runbook below.

    Affected
    • SonicWall Email Security eq 10.0.9 and earlier..10.0.9 and earlier

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

    Metrics

    9.8

    Priority

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

    Source: NVD, CVSS v3

    9.8

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: SingCERT, CVE.org

    88.8 %

    EPSS score

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

    Source: FIRST EPSS, percentile 99.78

    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
    253.65 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 exploitedSource: CSA/SingCERT How we classify
    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
    9.8 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
    9.8
    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“.

    Read in glossary
    88.8 %
    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
    99.78
    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 20 April 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-269

    Response and mitigation

    Why act now?

    Prioritisation rationale

    This flaw is network-reachable without authentication or user interaction and hands the attacker an administrator account directly. In practice it opens a chain with CVE-2021-20023 (file read) and CVE-2021-20022 (file upload) that ends in code execution on the gateway and theft of stored AD credentials. CISA flags known ransomware campaign use, and the vulnerability sits among those most likely to be exploited. Mail gateways are prime initial-access targets because they are internet-facing and wired into Active Directory. Treat any instance with an externally reachable admin UI as critical and requiring a compromise assessment, not just a patch. Internally restricted instances remain high priority until log review rules out earlier compromise.

    1. Runbook step 1

      Immediate response (0-24 h)

      • Inventory: Identify every SonicWall Email Security instance, covering hardware appliances (ESA 3300/4300/5000/5050/7000/7050/8300), virtual appliances and Windows software installs. Affected builds are 10.0.9.6103 (software) and 10.0.9.6105 (appliance firmware). SonicWall's hosted service is patched by the vendor and is out of scope for self-managed remediation.
      • Patch: The fix is available from the vendor. Look up the fixed build in the vendor advisory. Make sure the update closes the full chain, meaning CVE-2021-20021, CVE-2021-20022 and CVE-2021-20023 together.
      • Pull the management UI off the internet now: Restrict HTTP/HTTPS access to the admin web interface (TCP 80/443 by default, or your configured management port) to a dedicated management network or jump-host allowlist at the perimeter firewall. Leave SMTP (TCP 25) open for mail flow.
      • Audit administrator accounts: Compare all admin users and roles against your approved baseline. Disable unknown accounts rather than deleting them, preserve them as evidence, and trigger your incident process.
      • If compromise is suspected: Capture forensic evidence first (Tomcat logs, audit logs, web directories, and a memory image on Windows hosts) and isolate the appliance at the network level. Patching does not remove web shells that are already in place.
      • Rotate credentials: Change every secret stored on the appliance. This includes local admin passwords, the LDAP/AD bind account, SMTP relay and API credentials, and the local service account on Windows installs.

    2. Runbook step 2

      Mitigation layers

      • Network segmentation: Place the appliance in a DMZ with tight egress rules. Allow only SMTP to defined mail hops, DNS, NTP and vendor update servers, and block arbitrary outbound connections such as reverse shells or tool downloads. Limit traffic from the appliance zone into the internal network to the Exchange/M365 connector and LDAP(S) to named domain controllers.
      • WAF/reverse proxy: If the web UI must stay externally reachable (for example, end-user quarantine access), front it with an authenticating reverse proxy. Block unauthenticated POSTs to administrative paths. Also filter path-traversal patterns (../, %2e%2e) and ZIP uploads to branding functions, which relate to CVE-2021-20022/-20023.
      • IPS: Enable vendor signatures for CVE-2021-20021/-20022/-20023 in your IPS or Suricata ruleset where your product provides them, and switch them from alert to drop.
      • Endpoint hardening (Windows installs): Run EDR on the host. Use WDAC/AppLocker to stop the Tomcat/Java process from spawning shell interpreters. Run the service with minimal rights rather than LocalSystem where the vendor supports it.
      • IAM/least privilege: Keep the LDAP bind account read-only and out of privileged AD groups. Require admin access through an MFA-protected jump host.
      • Lifecycle: If the platform cannot be upgraded or is no longer maintained, prioritise replacing it with a supported mail security gateway.

    3. Runbook step 3

      Detection rules

      • New admin accounts (appliance audit log/syslog): Alert on account creation or role changes that have no matching change ticket. Treat it as especially suspicious when the creation is not preceded by a successful admin login. This requires syslog forwarding to the SIEM.
      • Web access logs (Tomcat/proxy): Look for unauthenticated POSTs to admin endpoints from external IPs, followed by a login from a newly created account. One SPL approach: index=proxy dest=<esa_ip> method=POST NOT src_ip IN (<mgmt_allowlist>) | stats count by src_ip, uri_path.
      • Web shell drops (Sysmon EID 11 / EDR file events): Flag new .jsp files under the Tomcat webapps directory outside update windows. Also flag files written with ../ path elements from extracted branding ZIPs.
      • Process ancestry (Sysmon EID 1 / Windows EID 4688): Sigma shape: ParentImage|endswith: '\java.exe' AND Image|endswith: ['\cmd.exe','\powershell.exe','\whoami.exe','\net.exe','\certutil.exe']. This is essentially never legitimate on an Email Security host.
      • Network (Zeek/Suricata/firewall): Watch for outbound sessions from the appliance to destinations outside your mail infrastructure. Also watch for unusual LDAP queries or SMB/RDP from the appliance into the internal network, which indicate lateral movement with harvested AD credentials.

    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

    A vulnerability in the SonicWall Email Security version 10.0.9.x allows an attacker to create an administrative account by sending a crafted HTTP request to the remote host.

    Source: CSA/SingCERT, CISA KEV Catalog, cvelistv5, NVD (NIST)

    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
    SonicWallEmail Security
    • 10.0.9 and earlier
    • —
    sonicwallemail_security
    • < 10.0.9.6103
    • 10.0.9.6103
    sonicwallemail_security_virtual_appliance
    • < 10.0.9.6105
    • 10.0.9.6105
    sonicwallhosted_email_security
    • < 10.0.9.6103
    • 10.0.9.6103

    Vendors and products

    Affected operating systems

    Affected operating systems
    Othersonicwallemail_security_appliance_3300_firmware—
    Othersonicwallemail_security_appliance_4300_firmware—
    Othersonicwallemail_security_appliance_5000_firmware—
    Othersonicwallemail_security_appliance_5050_firmware—
    Othersonicwallemail_security_appliance_7000_firmware—
    Othersonicwallemail_security_appliance_7050_firmware—
    Othersonicwallemail_security_appliance_8300_firmware—
    Othersonicwallemail_security_appliance_9000_firmware—

    Weakness classes (CWE)

    • CWE-269Improper Privilege Management

      Class

      The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.

      Entry at MITRE CWE-269

    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
    CSA/SingCERTZero-Day Vulnerabilities in SonicWall Email Security (opens in a new tab)CSA/SingCERTactively exploited

    References & sources

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