CVE-2017-18187 in ARM mbed TLS
Summary
by MITRE
In ARM mbed TLS before 2.7.0, there is a bounds-check bypass through an integer overflow in PSK identity parsing in the ssl_parse_client_psk_identity() function in library/ssl_srv.c.
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Analysis
by VulDB Data Team • 02/06/2023
The vulnerability identified as CVE-2017-18187 represents a critical security flaw in the mbed TLS cryptographic library that affects versions prior to 2.7.0. This issue manifests as a bounds-check bypass that occurs during the parsing of Pre-Shared Key (PSK) identities within the SSL/TLS handshake process. The flaw specifically resides in the ssl_parse_client_psk_identity() function located in the library/ssl_srv.c file, making it a core component of the library's SSL server functionality vulnerable to exploitation. The vulnerability's impact extends to any system utilizing mbed TLS for SSL/TLS operations where PSK authentication is implemented, potentially affecting a wide range of embedded systems, IoT devices, and network infrastructure components that rely on this cryptographic library for secure communications.
The technical root cause of this vulnerability stems from an integer overflow condition that occurs during the parsing of PSK identity data. When the ssl_parse_client_psk_identity() function processes incoming PSK identity information, it fails to properly validate the bounds of integer calculations used in the parsing logic. This integer overflow allows an attacker to manipulate the parsing process in such a way that bounds checks are effectively bypassed, enabling the execution of code that would normally be restricted by memory boundaries. The flaw essentially creates a scenario where malicious input can cause the parser to interpret memory locations incorrectly, potentially leading to memory corruption or arbitrary code execution. This type of vulnerability falls under CWE-190, which specifically addresses integer overflow conditions, and represents a classic example of how improper input validation can lead to serious security implications in cryptographic implementations. The vulnerability operates at the application layer within the SSL/TLS protocol stack, making it particularly dangerous as it can be exploited during the initial handshake phase when establishing secure connections.
The operational impact of CVE-2017-18187 extends beyond simple denial of service scenarios, as it can potentially enable remote code execution and privilege escalation attacks. An attacker who successfully exploits this vulnerability could manipulate the SSL/TLS handshake process to inject malicious data or bypass authentication mechanisms, particularly in systems that rely on PSK-based authentication. This vulnerability is particularly concerning for embedded systems and IoT devices that often use mbed TLS for secure communication but may have limited security updates and patching capabilities. The exploitation of this flaw could allow attackers to establish unauthorized secure connections, decrypt sensitive communications, or gain elevated privileges within affected systems. The vulnerability aligns with ATT&CK technique T1071.001 for application layer protocol usage and T1566 for credential access through social engineering or protocol manipulation, as it targets the fundamental authentication mechanisms within SSL/TLS implementations. Organizations using affected versions of mbed TLS should consider the potential for lateral movement within their networks and the possibility of establishing persistent backdoors through compromised secure communication channels.
The recommended mitigation for CVE-2017-18187 involves immediate upgrading to mbed TLS version 2.7.0 or later, which contains the necessary patches to address the integer overflow and bounds-check bypass conditions. System administrators should prioritize patching all affected systems, particularly those handling sensitive data or operating in high-security environments where PSK authentication is utilized. Additionally, organizations should implement network monitoring to detect unusual SSL/TLS handshake patterns that might indicate exploitation attempts, and consider implementing additional authentication layers or protocol restrictions to reduce the attack surface. Security teams should also conduct comprehensive vulnerability assessments to identify all systems using vulnerable versions of mbed TLS and ensure that proper security controls are in place to prevent exploitation. The fix implemented in version 2.7.0 specifically addresses the integer overflow condition in the PSK identity parsing logic, ensuring that proper bounds checking is maintained throughout the parsing process and preventing the bypass of memory safety mechanisms that could otherwise be exploited by malicious actors.