CVE-2017-7800 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur in WebSockets when the object holding the connection is freed before the disconnection operation is finished. This results in an 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-2017-7800 represents a critical use-after-free condition that manifests within the WebSocket implementation of Mozilla's browser engines. This flaw occurs during the disconnection process when the object managing the WebSocket connection is prematurely deallocated while asynchronous operations are still in progress. The technical nature of this vulnerability stems from improper memory management practices where the reference to the connection object is released before all pending operations can complete successfully. The issue affects multiple Mozilla products including Thunderbird versions prior to 52.3, Firefox Extended Support Release versions before 52.3, and standard Firefox versions before 55. This vulnerability is classified under CWE-416 as a use-after-free condition, which is a well-known class of memory safety issues that can lead to arbitrary code execution when exploited properly.
The operational impact of this vulnerability extends beyond simple application crashes to potentially enable remote code execution attacks. When the WebSocket connection object is freed while disconnection operations are still pending, subsequent operations on the freed memory can result in unpredictable behavior including heap corruption, information disclosure, or complete system compromise. Attackers can leverage this vulnerability by establishing a WebSocket connection to a target system and then triggering the disconnection sequence in a manner that causes the memory to be freed before operations complete. This creates an exploitable condition where attackers can manipulate the freed memory location to execute malicious code. The vulnerability aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as successful exploitation could allow attackers to execute arbitrary commands on affected systems through the browser engine.
Mitigation strategies for CVE-2017-7800 require immediate patching of affected software versions to address the underlying memory management flaw. Organizations should prioritize updating Thunderbird to version 52.3 or later, Firefox ESR to version 52.3 or later, and standard Firefox to version 55 or later. Additionally, network administrators should implement monitoring for suspicious WebSocket activity and consider deploying web application firewalls that can detect and block malicious WebSocket connections. The fix implemented by Mozilla addresses the core issue by ensuring proper reference counting and object lifecycle management during WebSocket disconnection operations, preventing the premature deallocation that previously led to exploitable conditions. Security teams should also conduct vulnerability assessments to identify any potentially compromised systems and implement network segmentation to limit the potential impact of successful exploitation attempts.