CVE-2019-25569 in Serial Terminal
Summary
by MITRE • 03/21/2026
RealTerm Serial Terminal 2.0.0.70 contains a stack-based buffer overflow vulnerability in the Echo Port field that allows local attackers to crash the application by triggering a structured exception handler (SEH) chain corruption. Attackers can craft a malicious input string with 268 bytes of padding followed by SEH overwrite values and paste it into the Port field to cause denial of service.
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Analysis
by VulDB Data Team • 03/27/2026
The vulnerability identified as CVE-2019-25569 resides within RealTerm Serial Terminal version 2.0.0.70, a widely used serial communication debugging tool that facilitates communication with embedded systems and hardware devices through serial ports. This application serves as a critical utility for developers and engineers working with embedded systems, IoT devices, and serial communication protocols, making its stability and security paramount for industrial and development environments. The vulnerability manifests in the Echo Port field handling mechanism, which represents a fundamental component of the application's serial communication interface where users configure port settings and communication parameters.
The technical flaw constitutes a stack-based buffer overflow that occurs when processing user input in the Echo Port field, specifically when the application fails to properly validate or limit the length of input data. This vulnerability directly maps to CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent memory locations on the program stack. The flaw is particularly dangerous because it enables structured exception handler (SEH) chain corruption, a technique commonly exploited in advanced exploit development where attackers manipulate the exception handling mechanism to redirect program execution flow. When a maliciously crafted input string containing 268 bytes of padding followed by carefully constructed SEH overwrite values is pasted into the Port field, the application's memory management becomes compromised, leading to unpredictable behavior and eventual application crash.
The operational impact of this vulnerability extends beyond simple denial of service, as it represents a significant security risk for development environments where RealTerm is actively used. Local attackers with access to the system can leverage this vulnerability to cause application instability, potentially disrupting critical development workflows or production debugging sessions. The vulnerability's exploitability is relatively straightforward, requiring only the ability to interact with the application's user interface and paste malicious input into the Echo Port field. This makes it particularly concerning in environments where multiple users may have access to the same system or where the application runs with elevated privileges. The SEH corruption technique employed in this exploit aligns with ATT&CK technique T1059.007, which covers scripting languages and command-line interpreters, though in this case the attack vector is more specifically targeting memory corruption within a GUI application.
Mitigation strategies for CVE-2019-25569 should focus on immediate remediation through official vendor patches or updates, as the vulnerability represents a fundamental memory safety issue that cannot be effectively addressed through configuration changes alone. Organizations should implement strict input validation measures for all user-supplied data, particularly in fields that handle serial port configurations and communication parameters. Additionally, system administrators should consider restricting local user access to applications with known memory corruption vulnerabilities, especially in production environments where stability is critical. The vulnerability highlights the importance of regular security assessments and vulnerability management processes, as it demonstrates how seemingly benign input fields can become attack vectors when proper bounds checking is absent. Security teams should also monitor for potential exploitation attempts in their environments and consider implementing application whitelisting policies to prevent unauthorized execution of vulnerable versions of RealTerm.