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Vulnerability record · CVE-2021-1567 · published 16 June 2021

CVE-2021-1567: Cisco anyconnect secure mobility client toctou race condition vulnerability

Cisco · Anyconnect Secure Mobility Client

A vulnerability in the DLL loading mechanism 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 a race condition in the signature verification process for DLL files that are loaded on an affected device. An attacker could exploit this vulnerability by sending a series of crafted interprocess communication (IPC) messages to the AnyConnect process. A successful exploit could allow the attacker to execute arbitrary code on the affected device with SYSTEM privileges. To exploit this vulnerability, the attacker must have valid credentials on the Windows system.

6.7 CVSS 3.1 Medium EPSS 0.18% · top 93.4% CWE-367 · TOCTOU race conditionCWE-427 · Uncontrolled search path element
6.7CVSS 3.1 base score, v2 6.2
0.18%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
17 Jun 2026Last modified by NVD

Description

A vulnerability in the DLL loading mechanism 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 a race condition in the signature verification process for DLL files that are loaded on an affected device. An attacker could exploit this vulnerability by sending a series of crafted interprocess communication (IPC) messages to the AnyConnect process. A successful exploit could allow the attacker to execute arbitrary code on the affected device with SYSTEM privileges. To exploit this vulnerability, the attacker must have valid credentials on the Windows system.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-anyconnect-pos-dll-ff8j6dFv Vendor Advisory
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-anyconnect-pos-dll-ff8j6dFv Vendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

7.8CVE-2020-3433Cisco AnyConnect Windows client DLL hijacking via IPC channelCisco AnyConnect Secure Mobility Client for Windows fails to properly validate resources loaded at run time, allowing a DLL hijacking attack through …KEVEPSS 10%analysed6.5CVE-2020-3153Cisco AnyConnect Windows Installer Path Handling Privilege EscalationThe Cisco AnyConnect Secure Mobility Client for Windows installer mishandles directory paths, letting an authenticated local user copy attacker-suppl…KEVEPSS 28%analysed9.3CVE-2012-3088Cisco anyconnect secure mobility client vulnerabilityCisco AnyConnect Secure Mobility Client 3.1.x before 3.1.00495, and 3.2.x, does not check whether an HTTP request originally contains ScanSafe header…EPSS 1.8%9.3CVE-2012-2493Cisco anyconnect secure mobility client improper input validation vulnerabilityThe VPN downloader implementation in the WebLaunch feature in Cisco AnyConnect Secure Mobility Client 2.x before 2.5 MR6 on Windows, and 2.x before 2…EPSS 3.9%9.3CVE-2011-2040Cisco anyconnect secure mobility client improper input validation vulnerabilityThe helper application in Cisco AnyConnect Secure Mobility Client (formerly AnyConnect VPN Client) before 2.5.3041, and 3.0.x before 3.0.629, on Linu…EPSS 11%7.8CVE-2023-20178Cisco anyconnect secure mobility client incorrect default permissions vulnerabilityA vulnerability in the client update process of Cisco AnyConnect Secure Mobility Client Software for Windows and Cisco Secure Client Software for Win…EPSS 5.4%7.8CVE-2021-40124Cisco anyconnect secure mobility client improper privilege management vulnerabilityA vulnerability in the Network Access Manager (NAM) module of Cisco AnyConnect Secure Mobility Client for Windows could allow an authenticated, local…EPSS 0.24%7.8CVE-2021-1430Cisco anyconnect secure mobility client uncontrolled search path element vulnerabilityMultiple vulnerabilities in the install, uninstall, and upgrade processes of Cisco AnyConnect Secure Mobility Client for Windows could allow an authe…EPSS 0.23%

Source: NIST National Vulnerability Database (record CVE-2021-1567), CISA KEV, FIRST EPSS (scores of 2026-10-02). This page is refreshed as NVD updates the record.