CVE-2025-20271Network attack vector

VPN service restart via uninitialized session state

Published Jun 18, 2025 · Updated Jun 18, 2025

Denial of service in Cisco Meraki MX Firmware allows remote attackers to restart the AnyConnect VPN server via crafted HTTPS requests. During SSL VPN session establishment, variable initialization errors cause the server to process a crafted request sequence with uninitialized state. Exposure requires AnyConnect VPN with client certificate authentication enabled; one exploit drops established sessions, while sustained requests block new connections.

CVSS severity8.6
High
EPSS probability0.55%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Cisco Meraki MX Firmware allows remote attackers to restart the AnyConnect VPN server via crafted HTTPS requests. During SSL VPN session establishment, variable initialization errors cause the server to process a crafted request sequence with uninitialized state. Exposure requires AnyConnect VPN with client certificate authentication enabled; one exploit drops established sessions, while sustained requests block new connections.

The record

CVE
CVE-2025-20271
Published
Jun 18, 2025
Updated
Jun 18, 2025
Vendor
ClamAV
Product
Cisco Meraki MX Firmware
Classifications
CWE-457, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 18, 2025CVE publishedPublication date reported by the CVE source.
  2. Jun 18, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

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 vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · Cisco Meraki MX Firmwareversion=N/A

Published CVSS scores

8.6Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/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)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-457Use of Uninitialized Variable
T1499.004Application or System Exploitation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo