Executive Summary
In March 2026, a critical integer underflow vulnerability (CVE-2026-25075) was identified in strongSwan versions 4.5.0 through 6.0.4, specifically within the EAP-TTLS AVP parser. This flaw allows unauthenticated remote attackers to crash the charon IKE daemon by sending crafted AVP data with invalid length fields during IKEv2 authentication, leading to a denial of service. The vulnerability arises from improper validation of AVP length fields, resulting in excessive memory allocation or NULL pointer dereference. (nvd.nist.gov)
The discovery of this vulnerability underscores the importance of rigorous input validation in security protocols. Organizations utilizing affected versions of strongSwan are urged to upgrade to version 6.0.5 or later to mitigate potential service disruptions. (nvd.nist.gov)
Why This Matters Now
This vulnerability highlights the critical need for organizations to promptly update their VPN solutions to prevent potential denial-of-service attacks that could disrupt business operations.
Attack Path Analysis
An unauthenticated attacker exploited an integer underflow vulnerability in strongSwan's EAP-TTLS AVP parser to crash the IKE daemon, causing a denial of service. This disruption prevented legitimate users from establishing VPN connections, impacting business operations.
Kill Chain Progression
Initial Compromise
Description
The attacker sends a crafted EAP-TTLS message with invalid length fields to the strongSwan VPN server, exploiting the integer underflow vulnerability.
Related CVEs
CVE-2026-25075
CVSS 7.5An integer underflow vulnerability in strongSwan's EAP-TTLS AVP parser allows unauthenticated remote attackers to cause a denial of service by sending crafted AVP data with invalid length fields during IKEv2 authentication.
Affected Products:
strongSwan strongSwan – 4.5.0 through 6.0.4
Exploit Status:
proof of concept
MITRE ATT&CK® Techniques
Endpoint Denial of Service
Exploitation for Client Execution
Exploit Public-Facing Application
Exfiltration Over Alternative Protocol
Application Layer Protocol
Potential Compliance Exposure
Mapping incident impact across multiple compliance frameworks.
PCI DSS 4.0 – Ensure all system components are protected from known vulnerabilities
Control ID: 6.2
NYDFS 23 NYCRR 500 – Cybersecurity Policy
Control ID: 500.03
DORA – ICT Risk Management Framework
Control ID: Article 5
CISA ZTMM 2.0 – Asset Management
Control ID: 3.1
NIS2 Directive – Cybersecurity Risk Management Measures
Control ID: Article 21
Sector Implications
Industry-specific impact of the vulnerabilities, including operational, regulatory, and cloud security risks.
Computer/Network Security
Critical VPN infrastructure vulnerability exposing security providers to denial of service attacks, potentially compromising client protection and incident response capabilities across managed environments.
Information Technology/IT
strongSwan CVE-2026-25075 threatens IT infrastructure stability through VPN service disruption, affecting remote access, business continuity, and encrypted communications for enterprise operations.
Government Administration
VPN authentication vulnerabilities pose significant risks to government networks, potentially disrupting secure communications, remote workforce access, and compliance with federal security requirements.
Financial Services
Integer underflow in VPN systems threatens secure financial communications and remote banking operations, potentially violating PCI compliance and disrupting critical financial infrastructure.
Sources
- strongSwan CVE-2026-25075: Integer Underflow in VPN Authenticationhttps://bishopfox.com/blog/strongswan-cve-2026-25075-integer-underflow-in-vpn-authenticationVerified
- NVD - CVE-2026-25075https://nvd.nist.gov/vuln/detail/CVE-2026-25075Verified
- strongSwan Vulnerability (CVE-2026-25075)https://www.strongswan.org/blog/2026/03/23/strongswan-vulnerability-(cve-2026-25075).htmlVerified
- VulnCheck Advisory: strongSwan EAP-TTLS AVP Parsing Integer Underflowhttps://www.vulncheck.com/advisories/strongswan-eap-ttls-avp-parsing-integer-underflowVerified
Frequently Asked Questions
Cloud Native Security Fabric Mitigations and ControlsCNSF
Aviatrix Zero Trust CNSF is pertinent to this incident as it embeds security directly into the cloud fabric, potentially reducing the attacker's ability to exploit vulnerabilities like the strongSwan EAP-TTLS AVP parser flaw, thereby limiting the blast radius of such attacks.
Control: Cloud Native Security Fabric (CNSF)
Mitigation: The attacker's ability to exploit the vulnerability may be constrained, reducing the likelihood of successful exploitation.
Control: Zero Trust Segmentation
Mitigation: The attacker's ability to escalate privileges may be constrained, reducing the likelihood of successful privilege escalation.
Control: East-West Traffic Security
Mitigation: The attacker's ability to move laterally may be constrained, reducing the likelihood of successful lateral movement.
Control: Multicloud Visibility & Control
Mitigation: The attacker's ability to establish command and control channels may be constrained, reducing the likelihood of successful command and control.
Control: Egress Security & Policy Enforcement
Mitigation: The attacker's ability to exfiltrate data may be constrained, reducing the likelihood of successful data exfiltration.
The attacker's ability to cause denial of service may be constrained, reducing the likelihood of successful service disruption.
Impact at a Glance
Affected Business Functions
- Remote Access Services
- Network Security Operations
Estimated downtime: 1 days
Estimated loss: $10,000
No data exposure; vulnerability leads to denial of service.
Recommended Actions
Key Takeaways & Next Steps
- • Upgrade strongSwan to version 6.0.5 or later to remediate the vulnerability.
- • Implement Egress Security & Policy Enforcement to monitor and control outbound traffic, mitigating potential exploitation attempts.
- • Deploy Threat Detection & Anomaly Response systems to identify and respond to unusual network activities indicative of exploitation attempts.
- • Utilize Multicloud Visibility & Control to gain comprehensive insights into network traffic and enforce security policies across cloud environments.
- • Regularly review and update security configurations to ensure compliance with Zero Trust principles and mitigate emerging threats.
