CVE-2019-8981 in axTLS
Summary
by MITRE
tls1.c in Cameron Hamilton-Rich axTLS before 2.1.5 has a Buffer Overflow via a crafted sequence of TLS packets because the need_bytes value is mismanaged.
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Analysis
by VulDB Data Team • 08/07/2023
The vulnerability identified as CVE-2019-8981 resides within the axTLS library version 2.1.4 and earlier, specifically in the tls1.c file where a buffer overflow condition occurs due to improper management of the need_bytes value during TLS packet processing. This flaw represents a critical security issue that can be exploited through the manipulation of TLS packet sequences, potentially allowing attackers to execute arbitrary code or cause denial of service conditions. The vulnerability stems from inadequate input validation and memory management within the TLS handshake process, particularly when handling fragmented or malformed TLS records.
The technical implementation of this buffer overflow occurs during the TLS protocol negotiation phase where the axTLS library incorrectly calculates or manages the number of bytes required for processing incoming TLS packets. When a malicious actor crafts a sequence of TLS packets with specific characteristics, the need_bytes value becomes mismanaged, leading to insufficient buffer allocation or incorrect boundary checking. This mismanagement allows an attacker to write data beyond the allocated buffer space, potentially overwriting adjacent memory locations and corrupting program execution flow. The vulnerability is classified under CWE-121 as a stack-based buffer overflow, which is a well-known weakness in memory safety that has been documented across numerous security frameworks and threat models.
From an operational perspective, this vulnerability poses significant risks to systems utilizing the affected axTLS library, particularly those implementing TLS 1.0 or 1.1 protocols where the library is used for secure communications. The impact extends beyond simple denial of service as successful exploitation could enable remote code execution, allowing attackers to gain unauthorized access to systems, steal sensitive data, or disrupt critical services. The vulnerability is particularly concerning because it can be triggered through network-based attacks without requiring authentication, making it an attractive target for automated exploitation campaigns. Security analysts should note that this flaw aligns with ATT&CK technique T1071.001 for application layer protocol usage and T1210 for exploitation of remote services, demonstrating how such vulnerabilities can be leveraged in broader attack chains.
Mitigation strategies for CVE-2019-8981 primarily focus on upgrading to axTLS version 2.1.5 or later, which includes patches addressing the buffer overflow condition through proper need_bytes value management and enhanced input validation. Organizations should also implement network segmentation and monitoring to detect anomalous TLS packet sequences that might indicate exploitation attempts. Additional protective measures include disabling vulnerable TLS versions, implementing strict packet filtering rules, and conducting regular security assessments of systems using the affected library. The vulnerability underscores the importance of maintaining up-to-date cryptographic libraries and following secure coding practices that prevent buffer overflow conditions through proper memory management and input validation mechanisms.