CVE-2026-92067 Overview
CVE-2026-92067 is a use-after-free vulnerability [CWE-416] in the Widget: Gtk component used by Mozilla Firefox and Thunderbird on Linux. The flaw allows memory to be referenced after it has been freed, which can lead to memory corruption and potentially arbitrary code execution within the browser or mail client process. Mozilla addressed the issue in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3.
Critical Impact
A successful exploit against the Gtk widget code can corrupt process memory, enabling attacker-controlled execution inside Firefox or Thunderbird when a user views crafted content.
Affected Products
- Mozilla Firefox versions prior to 156
- Mozilla Firefox ESR versions prior to 153.3
- Mozilla Thunderbird versions prior to 156 and prior to 153.3
Discovery Timeline
- 2026-09-15 - CVE-2026-92067 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-92067
Vulnerability Analysis
The vulnerability resides in the Widget: Gtk component, which provides the GTK-based windowing and widget layer for Firefox and Thunderbird on Linux. A use-after-free occurs when the code accesses a heap object after that object's memory has been released. The freed allocation may be reallocated for attacker-influenced data, allowing manipulation of function pointers or object state.
Because the Gtk widget layer processes rendering, input, and window lifecycle events, the freed object can be reached through interactions with page content, embedded frames, or message rendering in Thunderbird. Exploitation typically requires the victim to load a crafted page or open a crafted email that triggers the specific event sequence.
The EPSS probability for this issue is 0.144% with a percentile of 4.023, indicating no observed exploitation activity at publication.
Root Cause
The root cause is improper lifetime management of a heap-allocated object owned by the Gtk widget code. A reference to the object is retained and later dereferenced after the owning code has already freed it, violating the object's expected lifecycle.
Attack Vector
An attacker delivers crafted web content or HTML email that drives the Gtk widget code into the vulnerable state. In Firefox, this is reached by browsing to a malicious page. In Thunderbird, previewing or opening a crafted message can trigger the same code path. Mozilla has not published exploit details; refer to Mozilla Security Advisory MFSA-2026-90 and Mozilla Bug #2058664 for available technical context.
Detection Methods for CVE-2026-92067
Indicators of Compromise
- Unexpected crashes of firefox or thunderbird processes on Linux hosts, especially with SIGSEGV in Gtk-related frames.
- Crash reports referencing freed heap objects inside widget/gtk code paths.
- New or unusual child processes spawned by Firefox or Thunderbird following a browsing or mail-viewing session.
Detection Strategies
- Inventory installed Firefox, Firefox ESR, and Thunderbird versions across Linux endpoints and flag any build older than the fixed releases.
- Correlate browser or mail-client crash telemetry with subsequent process, file, or network activity to surface post-exploitation behavior.
- Alert on Firefox or Thunderbird processes writing to non-standard directories or executing shell interpreters.
Monitoring Recommendations
- Ingest endpoint process, file, and network telemetry into a central analytics platform to detect anomalous behavior originating from browser or mail-client processes.
- Track outbound connections from Firefox and Thunderbird to newly observed or low-reputation domains.
- Monitor package management logs on Linux hosts to verify that Mozilla security updates are applied within the expected patching window.
How to Mitigate CVE-2026-92067
Immediate Actions Required
- Upgrade Firefox to version 156 or later on all managed endpoints.
- Upgrade Firefox ESR deployments to version 153.3 or later.
- Upgrade Thunderbird to version 156 or Thunderbird ESR 153.3 or later.
- Restart affected applications after patching to ensure the vulnerable code is unloaded from memory.
Patch Information
Mozilla fixed the vulnerability in Firefox 156, Firefox ESR 153.3, Thunderbird 156, and Thunderbird 153.3. Details are published in Mozilla Security Advisory MFSA-2026-90, MFSA-2026-93, MFSA-2026-94, and MFSA-2026-96.
Workarounds
- No vendor-supplied workaround exists; apply the vendor patch as the primary remediation.
- Disable HTML rendering in Thunderbird and view messages as plain text to reduce exposure through email vectors until patching is complete.
- Restrict browsing to trusted sites and enforce enterprise browser policies that block untrusted content on unpatched hosts.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.