CVE-2025-62291 in strongSwan
Summary
by MITRE • 01/16/2026
In the eap-mschapv2 plugin (client-side) in strongSwan before 6.0.3, a malicious EAP-MSCHAPv2 server can send a crafted message of size 6 through 8, and cause an integer underflow that potentially results in a heap-based buffer overflow.
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Analysis
by VulDB Data Team • 03/13/2026
The vulnerability identified as CVE-2025-62291 affects the eap-mschapv2 plugin within strongSwan versions prior to 6.0.3, representing a critical security flaw in the client-side implementation of the Extensible Authentication Protocol with Microsoft Challenge Handshake Authentication Protocol version 2. This authentication mechanism is commonly used in virtual private network implementations to establish secure remote connections. The vulnerability stems from inadequate input validation within the EAP-MSCHAPv2 client-side processing logic, where the system fails to properly validate the size of incoming authentication messages before proceeding with memory allocation operations.
The technical exploitation of this vulnerability occurs when a malicious EAP-MSCHAPv2 server sends a specially crafted authentication message with a payload size ranging between 6 and 8 bytes. This specific message size triggers an integer underflow condition within the memory management routines of the strongSwan client. The integer underflow manifests when the system attempts to perform arithmetic operations on unsigned integer values, resulting in unexpected negative values that subsequently corrupt the heap memory structure. This memory corruption creates conditions where attackers can potentially execute arbitrary code or cause denial of service through controlled heap-based buffer overflow scenarios.
The operational impact of this vulnerability extends beyond simple authentication failures, as it represents a significant threat to the integrity and availability of VPN connections established through strongSwan implementations. Attackers exploiting this flaw could gain unauthorized access to secure network resources, potentially leading to data breaches, privilege escalation, or complete network compromise. The vulnerability affects organizations relying on strongSwan for their VPN infrastructure, particularly those implementing EAP-MSCHAPv2 authentication for remote access solutions. The heap-based buffer overflow condition creates opportunities for attackers to manipulate memory contents and potentially execute malicious code within the context of the strongSwan client process.
Security professionals should recognize this vulnerability as aligning with CWE-191, which specifically addresses integer underflow conditions, and CWE-119, covering the improper restriction of operations within a memory buffer. The vulnerability also maps to ATT&CK technique T1566, which involves social engineering through malicious authentication protocols, and T1071, covering application layer protocol usage for command and control communications. Organizations should prioritize immediate patching of affected strongSwan installations to version 6.0.3 or later, implementing network monitoring to detect potential exploitation attempts, and reviewing authentication configurations to minimize attack surface. Additional mitigations include implementing network segmentation, deploying intrusion detection systems, and conducting security audits of all VPN-related infrastructure to ensure comprehensive protection against similar authentication protocol vulnerabilities.