CVE-2016-20047 in Gadu
Summary
by MITRE • 03/28/2026
EKG Gadu 1.9~pre+r2855-3+b1 contains a local buffer overflow vulnerability in the username handling that allows local attackers to execute arbitrary code by supplying an oversized username string. Attackers can trigger the overflow in the strlcpy function by passing a crafted buffer exceeding 258 bytes to overwrite the instruction pointer and execute shellcode with user privileges.
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Analysis
by VulDB Data Team • 03/29/2026
The vulnerability identified as CVE-2016-20047 represents a critical local buffer overflow flaw within the EKG Gadu messaging application version 1.9~pre+r2855-3+b1. This security weakness resides in the application's username handling mechanism, specifically within the strlcpy function implementation. The flaw enables local attackers with user-level privileges to escalate their execution rights by crafting malicious input that exceeds the allocated buffer space. The vulnerability manifests when the application processes user-provided username strings without proper bounds checking, creating an exploitable condition that can be leveraged for arbitrary code execution.
The technical implementation of this vulnerability stems from improper buffer management within the strlcpy function, which is designed to safely copy strings while preventing buffer overflows. However, in this specific implementation, the function fails to properly validate input length against the allocated buffer boundaries. When an attacker supplies a username string exceeding 258 bytes, the function continues to copy data beyond the intended buffer limits, causing memory corruption that overwrites adjacent memory locations including the instruction pointer. This memory corruption directly enables attackers to redirect program execution flow and inject malicious shellcode that executes with the privileges of the affected user account.
The operational impact of this vulnerability extends beyond simple privilege escalation as it provides attackers with a persistent foothold within the system. Local attackers can leverage this vulnerability to execute arbitrary code in the context of the target user, potentially leading to complete system compromise if the affected user account possesses elevated privileges. The vulnerability's local nature means that exploitation requires physical access or prior unauthorized access to the system, but once exploited, attackers can maintain persistence and potentially escalate privileges further. The execution of shellcode with user privileges creates opportunities for attackers to establish backdoors, exfiltrate data, or deploy additional malicious payloads within the compromised environment.
Security professionals should implement multiple layers of mitigation to address this vulnerability effectively. The primary recommendation involves updating the EKG Gadu application to a patched version that properly implements bounds checking and secure string handling mechanisms. System administrators should also consider implementing privilege separation techniques to limit the impact of potential exploitation, ensuring that user accounts running the application operate with minimal necessary privileges. Additionally, monitoring for unusual username input patterns and implementing input validation controls can help detect and prevent exploitation attempts. Organizations should also conduct regular security assessments to identify similar buffer overflow vulnerabilities in other applications and ensure proper memory management practices are followed throughout their software development lifecycle. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of how improper input validation can lead to remote code execution vulnerabilities. The attack vector follows typical ATT&CK techniques for privilege escalation, specifically targeting local exploitation methods that leverage application-level vulnerabilities to gain elevated system access.