CVE-2025-20271 Cisco Meraki MX and Z Series AnyConnect VPN with Client Certificate Authentication Denial of Service Vulnerability
Unauthenticated remote attackers can cause a denial of service in Cisco Meraki AnyConnect VPN by sending crafted HTTPS requests, disrupting all active sessions.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-20271?
CVE-2025-20271 is a high-severity denial of service vulnerability in Cisco Meraki MX Firmware, published on 18 Jun 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
A vulnerability in the Cisco AnyConnect VPN server of Cisco Meraki MX and Cisco Meraki Z Series Teleworker Gateway devices could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the Cisco AnyConnect service on an affected device. This vulnerability is due to variable initialization errors when an SSL VPN session is established. An attacker could exploit this vulnerability by sending a sequence of crafted HTTPS requests to an affected device. A successful exploit could allow the attacker to cause the Cisco AnyConnect VPN server to restart, resulting in the failure of all established SSL VPN sessions and forcing remote users to initiate a new VPN connection and re-authenticate. A sustained attack could prevent new SSL VPN connections from being established, effectively making the Cisco AnyConnect VPN service unavailable for all legitimate users.
Weakness: CWE-457
Which versions are affected by CVE-2025-20271?
How do I fix CVE-2025-20271?
No fix has been published for CVE-2025-20271 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-20271 being exploited?
There is no known exploitation of CVE-2025-20271 in the wild and no public exploit code.
Sources
Also known as GHSA-m673-qg9w-p8mh.