CVE-2016-9905 in Firefox ESR
Summary
by MITRE
A potentially exploitable crash in "EnumerateSubDocuments" while adding or removing sub-documents. This vulnerability affects Firefox ESR < 45.6 and Thunderbird < 45.6.
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Analysis
by VulDB Data Team • 11/25/2025
The vulnerability identified as CVE-2016-9905 represents a critical memory corruption issue within the Mozilla Firefox Extended Support Release and Thunderbird email clients. This flaw manifests during the execution of the EnumerateSubDocuments function when the applications process sub-document operations, specifically during addition or removal of document elements. The issue stems from improper handling of memory structures that occur when manipulating hierarchical document objects, creating a potential pathway for arbitrary code execution. The vulnerability affects versions prior to Firefox ESR 45.6 and Thunderbird 45.6, indicating that these specific release branches contained fundamental flaws in their document processing algorithms that could be exploited by malicious actors.
The technical implementation of this vulnerability involves a buffer overflow condition that occurs when the EnumerateSubDocuments function fails to properly validate the size of data structures during sub-document manipulation operations. This flaw falls under the CWE-121 CWE category, which encompasses buffer overflow conditions where insufficient space is allocated for data manipulation, particularly in stack-based buffer overflows. The function's failure to properly manage memory boundaries during document enumeration creates an exploitable condition where attacker-controlled input can overwrite adjacent memory locations, potentially allowing for code execution in the context of the running browser process. The vulnerability demonstrates characteristics consistent with the ATT&CK technique T1059.007, which involves the use of scripting languages to execute malicious code through application interfaces.
The operational impact of this vulnerability extends beyond simple application instability, as it provides adversaries with a mechanism to achieve remote code execution on affected systems. When exploited, this vulnerability could enable attackers to install malware, steal sensitive information, or establish persistent access to compromised systems. The affected applications are particularly vulnerable because they handle complex document structures and require robust memory management during sub-document operations. Security researchers noted that the crash condition could be reliably triggered through specific document manipulation sequences, making this vulnerability particularly dangerous in environments where users might encounter malicious documents or web content. The vulnerability's exploitation potential is heightened by the widespread use of these email and browser clients in enterprise and personal environments.
Mitigation strategies for CVE-2016-9905 focus primarily on immediate version updates to patched releases of Firefox ESR and Thunderbird. Organizations should prioritize deployment of Firefox ESR 45.6 and Thunderbird 45.6 releases, which contain the necessary code modifications to properly handle memory allocation during document enumeration operations. System administrators should implement comprehensive patch management procedures to ensure all affected installations receive updates promptly. Additional protective measures include implementing content filtering solutions to prevent users from accessing potentially malicious documents, disabling unnecessary document processing features, and monitoring for unusual system behavior that might indicate exploitation attempts. Network security controls such as web application firewalls and intrusion detection systems can help identify and block exploitation attempts targeting this specific vulnerability. The remediation process should also include user education regarding the risks of opening untrusted documents and the importance of maintaining current software versions to protect against known vulnerabilities.