CVE-2014-1538 in Firefox
Summary
by MITRE
Use-after-free vulnerability in the nsTextEditRules::CreateMozBR function in Mozilla Firefox before 30.0, Firefox ESR 24.x before 24.6, and Thunderbird before 24.6 allows remote attackers to execute arbitrary code or cause a denial of service (heap memory corruption) via unspecified vectors.
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Analysis
by VulDB Data Team • 11/25/2025
The CVE-2014-1538 vulnerability represents a critical use-after-free flaw located within the nsTextEditRules::CreateMozBR function of Mozilla Firefox and Thunderbird applications. This vulnerability exists in versions prior to 30.0 for Firefox, 24.6 for Firefox ESR 24.x, and before 24.6 for Thunderbird, making it a significant security concern for users of these email and web browser applications. The flaw stems from improper memory management during the processing of HTML content, specifically when handling mozbr elements within text editing contexts. The vulnerability falls under CWE-416, which categorizes use-after-free conditions as a fundamental memory safety issue that can lead to unpredictable behavior and potential exploitation.
The technical implementation of this vulnerability involves a scenario where freed memory is accessed after the nsTextEditRules::CreateMozBR function completes its execution. When the function processes certain HTML constructs containing mozbr elements, it may prematurely release memory resources while other code paths still reference those locations. This creates a window where malicious content could manipulate the freed memory regions, potentially leading to arbitrary code execution or system instability. The heap memory corruption occurs because the application fails to properly track memory references during complex text editing operations, particularly when dealing with nested or malformed HTML structures that trigger the vulnerable code path.
Operational impact of this vulnerability extends beyond simple denial of service to encompass serious remote code execution capabilities. Attackers can craft malicious web pages or email content that, when processed by vulnerable applications, triggers the use-after-free condition. The exploitation process typically involves creating specific HTML constructs that force the browser or email client to execute the vulnerable function path, followed by memory manipulation techniques that leverage the freed heap space. This vulnerability aligns with ATT&CK technique T1059.007, which covers command and scripting interpreter execution through web-based interfaces, and can be particularly dangerous in targeted attacks where attackers seek to compromise user systems through email delivery methods. The risk is amplified by the fact that the vulnerability affects widely used applications that process untrusted content automatically.
Mitigation strategies for CVE-2014-1538 primarily focus on immediate patching and application updates to versions that contain the necessary memory management fixes. Users should upgrade to Firefox 30.0 or later, Firefox ESR 24.6 or later, and Thunderbird 24.6 or later where the vulnerability has been addressed through proper memory handling implementations. Organizations should implement network-level protections such as content filtering and web application firewalls to prevent exploitation of this vulnerability in environments where immediate patching is not feasible. Additionally, browser hardening techniques including sandboxing, memory protection mechanisms, and strict content security policies can provide additional defense-in-depth layers against potential exploitation attempts. The vulnerability demonstrates the importance of comprehensive memory safety testing and static code analysis in preventing such critical flaws that can be leveraged for remote code execution attacks.