CVE-2018-6459 in strongSwan
Summary
by MITRE
The rsa_pss_params_parse function in libstrongswan/credentials/keys/signature_params.c in strongSwan 5.6.1 allows remote attackers to cause a denial of service via a crafted RSASSA-PSS signature that lacks a mask generation function parameter.
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Analysis
by VulDB Data Team • 01/07/2020
The vulnerability identified as CVE-2018-6459 resides within the strongSwan cryptographic library version 5.6.1, specifically in the rsa_pss_params_parse function located in libstrongswan/credentials/keys/signature_params.c. This flaw represents a critical denial of service vulnerability that can be exploited by remote attackers through the careful crafting of RSASSA-PSS signatures. The vulnerability stems from insufficient input validation and parameter parsing within the cryptographic signature processing mechanism, which forms a fundamental component of the IPsec and IKE protocols that strongSwan implements for secure network communications.
The technical flaw manifests when the rsa_pss_params_parse function encounters a malformed RSASSA-PSS signature that is missing the mask generation function parameter. This parameter is essential for proper PSS signature verification according to pkcs#1 v2.1 standards, which specify the precise structure and requirements for RSASSA-PSS signatures. The function fails to properly validate the presence and correctness of this mandatory parameter, leading to a potential buffer over-read or improper memory access pattern that results in program termination. The vulnerability operates at the cryptographic parameter parsing layer, where the software assumes the presence of all required fields without adequate verification, creating a path for malformed inputs to disrupt normal operation.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged in broader network security attacks. When exploited, the denial of service condition affects the entire strongSwan daemon, potentially compromising the availability of IPsec VPN services that rely on this cryptographic library. This vulnerability is particularly concerning in environments where strongSwan is deployed as a critical infrastructure component for secure communications, as it could be used to disrupt business continuity or enable more sophisticated attacks. The attack vector requires only remote access to send maliciously crafted signatures, making it accessible to adversaries with minimal network proximity requirements, and aligns with ATT&CK technique T1499.004 for network denial of service attacks.
Mitigation strategies for CVE-2018-6459 should prioritize immediate patching of affected strongSwan installations to version 5.6.2 or later, which contains the necessary fixes for proper parameter validation. Organizations should also implement network monitoring to detect unusual signature parsing patterns that might indicate exploitation attempts, and consider deploying intrusion detection systems with signature rules specific to this vulnerability. Additionally, administrators should review their cryptographic configuration to ensure that only necessary signature algorithms are enabled, reducing the attack surface. The vulnerability demonstrates the importance of proper input validation in cryptographic libraries and aligns with CWE-248, which addresses the issue of an exception being thrown for an unknown error condition. Security teams should also consider implementing automated patch management processes to ensure timely remediation of similar vulnerabilities in cryptographic software components, as these types of flaws can have cascading effects across interconnected security systems that depend on robust cryptographic implementations.