CVE-2018-9989 in ARM mbed TLS
Summary
by MITRE
ARM mbed TLS before 2.1.11, before 2.7.2, and before 2.8.0 has a buffer over-read in ssl_parse_server_psk_hint() that could cause a crash on invalid input.
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Analysis
by VulDB Data Team • 06/05/2026
The vulnerability identified as CVE-2018-9989 affects the mbed TLS cryptographic library implementation used in various embedded and IoT devices, particularly those implementing the Transport Layer Security protocol. This issue manifests as a buffer over-read condition within the ssl_parse_server_psk_hint() function, which processes pre-shared key hints during TLS handshake operations. The flaw occurs when the library encounters malformed or invalid input data during the parsing of server pre-shared key hints, creating a scenario where the application attempts to read memory beyond the allocated buffer boundaries. This vulnerability impacts multiple versions of the library including those before 2.1.11, 2.7.2, and 2.8.0, representing a significant security concern for systems relying on mbed TLS for secure communications. The buffer over-read condition can lead to unpredictable behavior including application crashes, memory corruption, or potential information disclosure depending on the specific implementation and system architecture.
The technical nature of this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where an application accesses memory beyond the boundaries of a buffer. The flaw specifically occurs in the SSL/TLS handshake process when the mbed TLS library attempts to parse server pre-shared key hints without proper bounds checking. During normal operation, the library expects well-formed input data containing PSK hints, but when malformed data is provided, the parsing function fails to validate buffer limits properly. This allows an attacker to craft malicious TLS handshake messages that trigger the buffer over-read condition, potentially causing denial of service through application crashes or system instability. The vulnerability is particularly concerning in embedded systems where memory constraints and limited error handling capabilities may amplify the impact of such issues.
The operational impact of CVE-2018-9989 extends beyond simple denial of service scenarios, as it can compromise the overall security posture of affected systems. In environments where mbed TLS is used for secure communications, particularly in IoT devices, industrial control systems, or embedded networking equipment, this vulnerability creates opportunities for attackers to disrupt services or potentially gain unauthorized access. The crash condition can be exploited to create persistent denial of service attacks against critical infrastructure, while the memory corruption aspects could theoretically be leveraged for more advanced exploitation techniques. Organizations using affected versions of mbed TLS should consider the broader implications for their security infrastructure, as this vulnerability may be exploited in conjunction with other attack vectors to compromise system availability and integrity. The vulnerability affects systems across multiple industries including automotive, healthcare, manufacturing, and telecommunications where secure communications are paramount.
Mitigation strategies for CVE-2018-9989 primarily focus on upgrading to patched versions of the mbed TLS library, specifically versions 2.1.11, 2.7.2, or 2.8.0 and later. Organizations should conduct comprehensive inventory assessments to identify all systems utilizing affected library versions and prioritize patch deployment across their infrastructure. Network monitoring solutions should be enhanced to detect anomalous TLS handshake patterns that might indicate exploitation attempts, as the vulnerability can be triggered through malformed handshake messages. Additional defensive measures include implementing network segmentation to limit exposure, deploying intrusion detection systems with signature-based detection for known malicious TLS patterns, and establishing robust incident response procedures for handling potential exploitation attempts. System administrators should also consider implementing application-level firewalls or proxy services that can filter malformed TLS traffic before it reaches vulnerable endpoints, providing an additional layer of protection while patches are being deployed across the organization.