CVE-2026-109773 in Firefox
Summary
by MITRE • 10/13/2026
Denial-of-service in the Sync component. This vulnerability was fixed in Firefox 158.
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Analysis
by VulDB Data Team • 10/13/2026
The identified vulnerability resides within the synchronization subsystem of Mozilla Firefox, specifically affecting how data integrity and availability are managed during sync operations. As a denial-of-service flaw, this issue does not compromise confidentiality or integrity in the traditional sense but rather targets the availability component of the security triad. The root cause typically involves an improper handling of specific inputs or state transitions within the sync engine that can lead to resource exhaustion, infinite loops, or unhandled exceptions causing the application process to terminate unexpectedly. Such defects often arise when the software fails to validate input lengths, manage memory allocation correctly under high load, or handle edge cases in data parsing routines during the synchronization process with remote servers or local storage backends.
From a technical perspective, this type of vulnerability is frequently categorized under CWE-400, which covers Uncontrolled Resource Consumption, or potentially CWE-20 if it involves improper input validation that leads to application crashes. In the context of modern threat modeling and adversary behavior frameworks like MITRE ATT&CK, this flaw aligns with techniques related to Service Stop (T1529) or Impact via Denial of Service. An attacker who can trigger this condition might do so by crafting malicious sync payloads, manipulating local database states that are pushed during synchronization, or exploiting race conditions in the background processing threads responsible for merging remote changes with local data. The exploitability depends heavily on whether an external actor can influence the sync process directly, such as through a compromised account, injected bookmarks, history entries, or passwords designed to trigger the faulty code path.
The operational impact of this vulnerability is primarily disruptive rather than destructive in terms of data loss. When triggered, it results in the abrupt termination of the Firefox browser process, leading to a loss of unsaved work and requiring manual restart by the user. In enterprise environments where synchronization is critical for maintaining consistent configurations across devices, repeated denial-of-service events can significantly degrade productivity and increase helpdesk support costs. Furthermore, if the vulnerability allows for sustained resource consumption without crashing but rather causing severe lag or unresponsiveness, it effectively renders the browser unusable until system resources are freed or the process is killed manually. This impacts both individual users relying on seamless cross-device continuity and organizations depending on automated sync workflows for policy enforcement and data consistency.
Mitigation strategies focus primarily on timely patching as this issue has been resolved in Firefox version 158. Administrators should ensure that all client systems are updated to the latest stable release of Firefox to incorporate the code fixes addressing the resource management flaws within the sync component. For environments where immediate updating is not feasible, network-level controls such as web content filtering or proxy rules can be employed to restrict access to specific endpoints if the vulnerability is known to be triggered by remote server responses, although this is less common for client-side synchronization bugs. Additionally, enabling automatic update notifications ensures that users are promptly alerted when new versions become available. Security teams should also monitor internal logs for unusual spikes in browser crashes or process terminations associated with Firefox processes, which could indicate exploitation attempts against unpatched systems within the network infrastructure.