CVE-2021-1567

SYSTEM code execution via DLL verification race

Published Jun 16, 2021 · Updated Nov 7, 2024

DLL hijacking in Cisco Secure Client before 4.10.01075 allows local users to execute code as SYSTEM when the HostScan module is installed. A race separates DLL signature verification from loading, allowing crafted IPC messages to substitute code during that interval. Exploitation requires valid local credentials and the VPN Posture (HostScan) Module; Linux, macOS, ISE Posture-only, and mobile clients are unaffected.

CVSS severity7.0
High
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

DLL hijacking in Cisco Secure Client before 4.10.01075 allows local users to execute code as SYSTEM when the HostScan module is installed. A race separates DLL signature verification from loading, allowing crafted IPC messages to substitute code during that interval. Exploitation requires valid local credentials and the VPN Posture (HostScan) Module; Linux, macOS, ISE Posture-only, and mobile clients are unaffected.

The record

CVE
CVE-2021-1567
Published
Jun 16, 2021
Updated
Nov 7, 2024
Vendor
ClamAV
Product
Cisco Secure Client
Classifications
CWE-367, CAPEC-29, T1574.002
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Jun 16, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 7, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

ClamAV · Cisco Secure Clientversion=n/a

Published CVSS scores

7.0Cisco Systems, Inc.CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:X/RL:X/RC:X

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
CAPEC-29Leveraging Time-of-Check and Time-of-Use (TOCTOU) Race Conditions
T1574.002DLL Side-Loading

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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