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Public proof of conceptFix available

CVE-2021-1366

A public proof of concept exists; no exploitation attested.

  • Published2021-02-17
  • Fixed in4.9.05042
  • WeaknessCWE-347 · CWE-427

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2021-02-1717:15CVE publishedNVD
  2. 2026-10-2319:23First public proof of conceptPoC-in-GitHub

Observed activity

isMalicious corpus · updated 2026-10-23 21:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-1366?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-1366?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Cisco anyconnect secure mobility client
BranchAffectedFixed in
4.9< 4.9.050424.9.05042

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

  1. Update Cisco anyconnect secure mobility client to 4.9.05042

Advisories and patches

Detection

read 2026-10-23 19:23 UTC
Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
1 repository, unverifiedkoztkozt/CVE-2021-1366
PoC-in-GitHub

Sources

  • CISA-ADPSSVC decisionnone2024-11-08
  • OpenCVESSVC decisionnone—
  • CNACVSS 3.17.8read 2026-10-23
  • NVDCVSS 3.17.8read 2026-10-23
  • NVDCVSS 2.06.9read 2026-10-23
  • CNAweakness (CWE)CWE-347read 2026-10-23
  • NVDweakness (CWE)CWE-427read 2026-10-23
  • FIRST EPSSEPSS score1.3 %2026-10-22
  • PoC-in-GitHubproof of concept1read 2026-10-23

Technical details

CVSS v3 Vector
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Published
2021-02-17
Last Modified
2026-06-17
NVD status
Modified

Frequently asked questions

What is CVE-2021-1366?

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.

Is CVE-2021-1366 actively exploited?

Active exploitation of CVE-2021-1366 has not been confirmed. Its EPSS score was 1.3% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-1366?

CVE-2021-1366 has a CVSS v3 base score of 7.8 (HIGH severity), with vector string CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.

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