CVE-2018-5103 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur during mouse event handling due to issues with multiprocess support. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.6, Firefox ESR < 52.6, and Firefox < 58.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5103 represents a critical use-after-free condition that emerges during mouse event processing within browser environments that support multiprocess architecture. This flaw specifically manifests when the application handles mouse events in a multiprocess context, creating a scenario where memory previously freed by one process or thread is accessed by another, potentially leading to arbitrary code execution. The vulnerability affects major browser implementations including Thunderbird versions prior to 52.6, Firefox Extended Support Release versions before 52.6, and standard Firefox versions before 58, indicating a widespread impact across Mozilla's product ecosystem during a critical development phase.
The technical root cause of this vulnerability stems from improper memory management during the handling of mouse events in multiprocess environments where separate processes manage different aspects of browser functionality. When a mouse event occurs, the system allocates memory structures to process these events, but under certain conditions the memory management system fails to properly track the lifecycle of these objects. This results in a scenario where an object is freed from memory while references to it still exist, creating a use-after-free condition that can be exploited by malicious actors to execute arbitrary code. The multiprocess nature of modern browsers compounds this issue as communication between processes requires careful memory management that becomes vulnerable when event handling logic contains race conditions or improper reference counting.
The operational impact of CVE-2018-5103 extends beyond simple crash conditions to represent a serious security risk that could enable remote code execution on affected systems. Attackers could potentially craft malicious web content or phishing pages that, when viewed in vulnerable browsers, would trigger the use-after-free condition and allow for arbitrary code execution with the privileges of the browser process. This vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions, and represents a classic example of how multiprocess architecture can introduce complex memory management challenges. The vulnerability's exploitability is enhanced by the fact that it occurs during normal user interaction with mouse events, making it particularly dangerous as users may unknowingly trigger the exploit through routine browsing activities.
Mitigation strategies for CVE-2018-5103 primarily focus on immediate version updates to patched releases of the affected software. Organizations should prioritize updating Thunderbird to version 52.6 or later, Firefox ESR to version 52.6 or later, and standard Firefox to version 58 or later to eliminate the vulnerability. Additionally, security administrators should implement network-level protections such as content filtering and web application firewalls to reduce the risk of exploitation. From an ATT&CK perspective, this vulnerability maps to techniques involving exploitation of remote code execution vulnerabilities and privilege escalation, with the attack surface expanding through web-based delivery mechanisms. System administrators should also consider implementing sandboxing measures and privilege separation to limit the potential impact of successful exploitation, though the most effective mitigation remains timely patch deployment.