CVE-2018-5099 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when the widget listener is holding strong references to browser objects that have previously been freed, resulting in a potentially exploitable crash when these references are used. 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-2018-5099 represents a critical use-after-free condition that manifests within Mozilla's browser engine implementation. This flaw occurs in the interaction between widget listeners and browser objects, creating a scenario where references to previously deallocated memory structures remain active in memory. The technical nature of this vulnerability stems from improper memory management practices where the system fails to properly invalidate references to objects that have already been freed, leading to potential exploitation through memory corruption.
The core technical flaw involves the widget listener component maintaining strong references to browser objects that have undergone deallocation. When these freed objects are subsequently accessed through the retained references, the system attempts to operate on memory that has already been reclaimed, creating a use-after-free condition. This type of vulnerability falls under CWE-416, which specifically addresses the use of freed memory, and represents a classic memory safety issue that has been documented extensively in cybersecurity literature. The vulnerability affects multiple Mozilla products 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 the browser ecosystem.
The operational impact of this vulnerability extends beyond simple application instability, as it presents a potential pathway for remote code execution. When exploited, the use-after-free condition can lead to arbitrary code execution within the context of the affected browser or email client. Attackers can leverage this vulnerability to execute malicious code on target systems, potentially leading to complete system compromise. The vulnerability's exploitability is enhanced by the fact that it occurs during normal user interaction with browser objects, making it difficult to detect and prevent through standard security measures. This aligns with ATT&CK technique T1059, which covers command and scripting interpreter usage, as attackers can potentially use this vulnerability to establish persistent access through malicious code execution.
Mitigation strategies for CVE-2018-5099 primarily focus on immediate patch deployment and system updates. Organizations must prioritize updating all affected versions of Thunderbird, Firefox ESR, and Firefox to their respective patched versions. Additionally, implementing memory safety monitoring tools and runtime protections can help detect and prevent exploitation attempts. Network-level defenses such as web application firewalls and intrusion detection systems should be configured to monitor for suspicious activity patterns associated with memory corruption exploits. Security teams should also conduct thorough vulnerability assessments to identify any systems running unpatched versions of the affected software. The remediation process requires careful coordination to ensure that updates do not introduce compatibility issues while maintaining the security posture of the affected systems.