CVE-2018-12377 in Thunderbird
Summary
by MITRE
A use-after-free vulnerability can occur when refresh driver timers are refreshed in some circumstances during shutdown when the timer is deleted while still in use. This results in a potentially exploitable crash. This vulnerability affects Firefox < 62, Firefox ESR < 60.2, and Thunderbird < 60.2.1.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a critical use-after-free condition that manifests during the browser shutdown process when refresh driver timers are being refreshed. The flaw occurs when the system attempts to delete a timer object while it is still actively in use, creating a scenario where memory that has been freed is subsequently accessed by the application. This type of vulnerability falls under the category of memory safety issues and is particularly dangerous because it can lead to arbitrary code execution when exploited by malicious actors. The vulnerability affects Mozilla Firefox versions prior to 62, Firefox ESR versions prior to 60.2, and Thunderbird versions prior to 60.2.1, indicating a widespread impact across multiple Mozilla products that rely on similar timer management mechanisms.
The technical implementation of this vulnerability involves the refresh driver component of the browser's rendering engine, which manages periodic updates and animations. During the shutdown sequence, when the browser attempts to clean up timer resources, a race condition can occur where the timer deletion process conflicts with active timer callbacks. This creates a window where the timer object's memory is freed but the system continues to reference it, leading to potential memory corruption. The vulnerability is classified as a CWE-416 Use After Free, which is a well-known weakness in software security where memory is accessed after it has been freed by the program. This specific implementation pattern demonstrates a failure in proper resource management during application lifecycle events, particularly shutdown procedures.
The operational impact of this vulnerability is significant as it can be exploited to achieve remote code execution on affected systems. Attackers can craft malicious web content or phishing emails that trigger the vulnerable code path during browser shutdown, potentially leading to complete system compromise. The vulnerability's exploitability is enhanced by the fact that it occurs during normal browser operation, making it difficult to detect and prevent through standard security measures. This aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter, as successful exploitation could allow attackers to execute arbitrary commands on the target system. The vulnerability represents a critical risk for users who frequently browse the internet or receive email communications, as the attack surface is broad and the exploitation can occur through standard web browsing activities.
Mitigation strategies for this vulnerability should focus on immediate patching of affected software versions to ensure proper timer cleanup during shutdown processes. Organizations should implement comprehensive update management procedures to deploy security patches across all affected systems as quickly as possible. Additionally, browser hardening measures such as sandboxing, content security policies, and strict memory access controls can help reduce the potential impact of exploitation attempts. Network-based defenses including web application firewalls and intrusion detection systems should be configured to monitor for suspicious activities that might indicate exploitation attempts. The vulnerability serves as a reminder of the importance of proper resource management in software development, particularly during application lifecycle events, and underscores the need for thorough security testing of shutdown and cleanup procedures. System administrators should also consider implementing user education programs to raise awareness about the risks of visiting untrusted websites and opening suspicious email attachments that could trigger such exploits.