CVE-2018-5102 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when manipulating HTML media elements with media streams, resulting 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-2018-5102 represents a critical use-after-free flaw that manifests during the manipulation of HTML media elements when media streams are involved. This issue arises from improper memory management within the affected web browsers, specifically when handling multimedia content through the HTML5 media API. 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. The flaw stems from the browser's handling of media streams and their interaction with HTML media elements, creating a scenario where freed memory locations are accessed after being deallocated. This memory corruption vulnerability can be exploited by malicious actors to execute arbitrary code on affected systems, making it particularly dangerous for users who frequently interact with web content containing multimedia elements.
The technical nature of this vulnerability aligns with CWE-416, which specifically addresses use-after-free conditions in software development. This weakness occurs when a program continues to reference memory after it has been freed, creating opportunities for attackers to manipulate memory contents or trigger crashes that can be leveraged for exploitation. The vulnerability operates through the browser's media processing pipeline where HTML media elements such as video and audio tags interact with media streams, typically through JavaScript APIs. When these elements are manipulated in certain ways, particularly during rapid creation and destruction of media resources, the underlying memory management system fails to properly track references, leading to the freeing of memory that subsequent operations attempt to access. This creates a race condition scenario where the timing of memory deallocation and access can be manipulated by attackers to achieve code execution.
The operational impact of CVE-2018-5102 extends beyond simple browser crashes, presenting significant security risks to users of affected software versions. Attackers can craft malicious web pages that, when loaded in vulnerable browsers, trigger the use-after-free condition and potentially execute arbitrary code with the privileges of the browser process. This could lead to complete system compromise, especially when users visit malicious websites or open compromised email attachments in Thunderbird. The vulnerability is particularly concerning because it affects both desktop browsers and email clients that share common rendering engines, expanding the attack surface considerably. The exploitation typically requires a sophisticated attack vector involving crafted HTML content that specifically targets the media element manipulation paths within the browser's JavaScript engine, making it a targeted threat rather than a broad-based vulnerability.
Mitigation strategies for CVE-2018-5102 primarily focus on immediate software updates and patches provided by the affected vendors. Organizations should prioritize updating all affected systems to versions that include fixes for this vulnerability, specifically upgrading to Thunderbird 52.6 or later, Firefox ESR 52.6 or later, and Firefox 58 or later. Additionally, implementing browser security measures such as sandboxing, content security policies, and restricting access to potentially malicious web content can provide additional layers of protection. Network administrators should consider implementing web filtering solutions that can block access to known malicious domains and monitor for suspicious media content. From an operational security perspective, users should be educated about the risks of visiting untrusted websites and opening email attachments from unknown sources. The vulnerability also highlights the importance of regular security updates and patch management processes, as this type of memory corruption issue typically requires immediate attention due to its exploitable nature and potential for remote code execution. Security teams should monitor for indicators of compromise related to this vulnerability and ensure that their incident response procedures include specific guidance for handling use-after-free exploits.