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Critical Cisco AnyConnect Vulnerability Remote Access Threat

Redoracle TeamOriginal6/22/25About 2 minNewsvulnerabilityremote accessdenial of serviceCisco Merakifirmware

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Introduction

A critical security vulnerability in Cisco Meraki MX and Z Series devices has been identified, allowing unauthenticated attackers to launch denial of service (DoS) attacks against AnyConnect VPN services. This vulnerability, tracked as CVE-2025-20271, poses a high severity risk to organizations relying on these devices for secure remote access.

Key Highlights

  • Nature of the Vulnerability:
    • The vulnerability stems from variable initialization errors during SSL VPN session establishment on affected devices.
    • Attackers can exploit this flaw by sending crafted HTTPS requests to devices running AnyConnect VPN with client certificate authentication enabled.
  • Impact of Exploitation:
    • Successful exploitation results in the AnyConnect VPN server restarting, terminating all active SSL VPN sessions.
    • Continuous attacks could render the AnyConnect VPN service completely unavailable, disrupting legitimate user connections.
  • Affected Products:
    • The vulnerability affects various Cisco Meraki devices, including models from the MX Series (e.g., MX64, MX65, MX67, MX68) and Z Series (e.g., Z3, Z4).
    • Devices are vulnerable if they run specific firmware versions and have AnyConnect VPN with client certificate authentication enabled.
  • Mitigation Strategies:
    • Cisco has released software updates to address the vulnerability in firmware versions 18.107.13, 18.211.6, and 19.1.8.
    • Patching is the only effective mitigation strategy as no workarounds are available.
  • Broader Implications:
    • The discovery of this vulnerability emphasizes the need for enhanced vulnerability monitoring beyond traditional network perimeters.
    • As remote work continues to rise, securing VPN services is crucial for business operations.

Insights & Analysis

The vulnerability's classification under CWE-457 highlights the importance of proper variable initialization during connection processes. Exploiting this vulnerability can lead to severe disruptions in VPN services, impacting organizations' ability to maintain secure remote access.

Impact

The potential exploitation of this vulnerability can have far-reaching consequences for organizations relying on Cisco Meraki devices for remote access. Immediate action is necessary to apply the provided software updates and safeguard critical network infrastructure.

Conclusion

Organizations must prioritize timely updates to protect their network infrastructure and prevent service disruptions. The complexity of securing modern VPN implementations underscores the need for vigilant firmware management and integrated defense strategies. Stay informed and take proactive measures to mitigate risks associated with this critical vulnerability.

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