CVE-2017-7809 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur when an editor DOM node is deleted prematurely during tree traversal while still bound to the document. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-7809 represents a critical use-after-free condition within the Gecko rendering engine that powers Mozilla Firefox and Thunderbird applications. This flaw occurs during the manipulation of Document Object Model nodes within the browser's internal structure, specifically when an editor DOM node undergoes premature deletion while still maintaining active references within the document tree. The technical implementation involves the browser's tree traversal mechanisms failing to properly manage reference counts or object lifecycle management when nodes are removed from the DOM structure. This improper handling creates a scenario where memory previously allocated to a DOM node object becomes available for reuse while the application continues to reference the freed memory location, leading to unpredictable behavior and potential code execution.
The operational impact of this vulnerability extends beyond simple application instability, as it presents a significant exploitation vector for malicious actors seeking to compromise user systems. When the use-after-free condition manifests, it typically results in a crash that can be leveraged to execute arbitrary code within the context of the affected application. The vulnerability's exploitation potential is heightened by the fact that it occurs in the core rendering engine where user-generated content is processed, making it particularly dangerous in web browsing scenarios. Attackers can craft malicious web pages that trigger the specific code path leading to the premature deletion of DOM nodes, followed by attempts to access the freed memory, potentially enabling remote code execution. This vulnerability affects multiple versions of Mozilla's browser suite, with the impact extending to Thunderbird email client and both regular Firefox releases and Firefox Extended Support Release versions up to specific patch levels.
Security professionals should recognize this vulnerability as a variant of CWE-416, which specifically addresses use-after-free conditions in memory management. The flaw demonstrates characteristics consistent with ATT&CK technique T1059, where adversaries leverage application vulnerabilities to execute malicious code through compromised software components. The affected software versions represent a window of opportunity for exploitation where the proper memory management protocols were not fully implemented or maintained during DOM node manipulation. Organizations should prioritize immediate patching of all affected versions, as the vulnerability does not require user interaction beyond visiting a malicious webpage or opening a specially crafted email message. The remediation strategy involves updating to patched versions of Firefox and Thunderbird where the DOM node management and tree traversal algorithms have been corrected to properly handle object lifecycle management and prevent premature memory deallocation while references remain active. Additionally, implementing network-level protections such as web application firewalls and content filtering systems can provide additional defense-in-depth measures while awaiting full patch deployment across all affected systems.