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Anyconnect Secure Mobility ClientApplication · Cisco

CVE-2021-1366

HIGH · 7.8 CVSS v3.1 Published 2021-02-17
Fix available
A fix is available. Upgrade to 4.9.05042 or later.
See remediation →
80/100
Remediation priority · High
Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
A vulnerability in the interprocess communication (IPC) channel of Cisco AnyConnect Secure Mobility Client for Windows could allow an authenticated, local attacker to perform a DLL hijacking attack on an affected device if the VPN Posture (HostScan) Module is installed on the AnyConnect client. This vulnerability is due to insufficient validation of resources that are loaded by the application at run time. An attacker could exploit this vulnerability by sending a crafted IPC message to the AnyConnect process. A successful exploit could allow the attacker to execute arbitrary code on the affected machine with SYSTEM privileges. To exploit this vulnerability, the attacker needs valid credentials on the Windows system.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A DLL hijacking vulnerability exists in the IPC channel of Cisco AnyConnect Secure Mobility Client for Windows when the VPN Posture (HostScan) Module is installed. An authenticated local attacker with valid Windows credentials can send a crafted IPC message to the AnyConnect process, causing it to load a malicious DLL and execute arbitrary code with SYSTEM privileges.

MitigationApply the vendor patch from Cisco when available. Until then, restrict local access to privileged accounts, monitor for suspicious DLL loading activity, and consider disabling the HostScan module if not required.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Anyconnect Secure Mobility ClientApplication
Affected:< 4.9.05042

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify installed Cisco AnyConnect version
    Open Windows Programs and Features or run 'wmic product get name,version' to find Cisco AnyConnect Secure Mobility Client and note its version number
    Affected if The installed version is less than 4.9.05042 (for example, 4.8.x, 4.7.x, etc.)
  2. Verify HostScan module presence
    Check for the HostScan or VPN Posture module component within the Cisco AnyConnect installation directory or via Add/Remove Programs features
    Affected if The HostScan/VPN Posture module is installed and listed as a component of the AnyConnect deployment
  3. Confirm AnyConnect service runs as SYSTEM
    Open Windows Services console, locate the Cisco AnyConnect Service, right-click and view Properties to check the Log On account
    Affected if The service runs under SYSTEM or LocalSystem account (this confirms the privilege level that could be obtained)
  4. Inspect IPC channel configuration
    Review AnyConnect configuration files in the installation directory for IPC channel settings related to HostScan functionality
    Affected if HostScan IPC channel is enabled in the configuration (allows the attack vector)

You are affected if Cisco AnyConnect Secure Mobility Client version is below 4.9.05042 AND the HostScan/VPN Posture module is installed on your Windows system.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 4.9.05042 or later
Fixed in 4.9.05042
Interim mitigation

Apply the vendor patch from Cisco when available. Until then, restrict local access to privileged accounts, monitor for suspicious DLL loading activity, and consider disabling the HostScan module if not required.

Fix this in Anyconnect Secure Mobility Client Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing4.0 h
  • Review / QA2.0 h
9.0 hours of engineering $1,540
Get the upgrade done

An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $2,464.

Scan for this in your stack

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-1366 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data