CVE-2026-92024: Firefox SVG Use-After-Free Vulnerability

CVE-2026-92024 Overview

CVE-2026-92024 is a use-after-free vulnerability in the Scalable Vector Graphics (SVG) component of Mozilla Firefox and Thunderbird. The flaw allows memory to be referenced after it has been freed, a class of memory corruption issue that commonly leads to browser crashes or code execution in the content process. Mozilla addressed the defect across multiple release channels, including Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. The issue is tracked in Mozilla Bug #2068354 and referenced in advisories MFSA-2026-90 through MFSA-2026-96.

Critical Impact
Rendering a crafted SVG document may trigger memory corruption inside the browser content process, creating conditions suitable for exploitation.

Affected Products

Mozilla Firefox versions prior to 156
Mozilla Firefox ESR versions prior to 115.41, 140.16, and 153.3
Mozilla Thunderbird versions prior to 156, 140.16, and 153.3

Discovery Timeline

2026-09-15 - CVE-2026-92024 published to NVD
2026-09-16 - Last updated in NVD database

Technical Details for CVE-2026-92024

Vulnerability Analysis

The vulnerability resides in the SVG rendering component shared by Firefox and Thunderbird. A use-after-free condition occurs when the code retains a reference to memory that has already been released back to the allocator. When the freed memory is reused for a different object, subsequent access through the stale pointer operates on unrelated data.

In browser engines, SVG parsing and layout involve complex object lifetimes across DOM nodes, frames, and rendering primitives. Reentrancy through script or layout callbacks can free an object while a parent routine still holds a raw pointer to it. Attackers who control the SVG content can groom the heap to place attacker-influenced data into the reclaimed slot.

Root Cause

The root cause is improper lifetime management inside the SVG component, resulting in a dangling reference. Mozilla has not published full technical details in the public NVD entry. Refer to Mozilla Bug #2068354 and the corresponding Mozilla Security Advisory MFSA-2026-90 for the underlying patch discussion.

Attack Vector

Exploitation requires a target user to load attacker-controlled SVG content in an affected build. Delivery vectors include navigation to a malicious web page, an SVG embedded in an HTML email rendered by Thunderbird, or a document that embeds an SVG resource. Successful triggering can crash the content process and, depending on heap state, may enable arbitrary code execution within the sandboxed renderer.

No public proof-of-concept or exploit code is available at the time of publication. See the Mozilla Security Advisory MFSA-2026-91 and related MFSA entries through MFSA-2026-96 for vendor guidance.

Detection Methods for CVE-2026-92024

Indicators of Compromise

Unexpected crashes of firefox.exe, firefox-bin, or thunderbird processes with signatures consistent with heap corruption during SVG rendering.
Presence of crash reports referencing SVG frame, DOM, or layout classes in Mozilla crash telemetry.
Web or mail content containing unusually complex or malformed SVG payloads delivered to users on unpatched builds.

Detection Strategies

Inventory Firefox and Thunderbird installations across the environment and flag versions below the fixed releases listed in the advisories.
Monitor endpoint telemetry for browser or mail client child-process crashes correlated with SVG or graphics module frames.
Inspect proxy and email gateway logs for delivery of .svg attachments or SVG-heavy web content from untrusted origins.

Monitoring Recommendations

Enable and centralize browser crash reporting to identify recurring content-process failures on unpatched hosts.
Alert on post-crash spawn of unusual child processes from firefox or thunderbird, which may indicate successful exploitation.
Track patch compliance for Mozilla products through configuration management and vulnerability scanners.

How to Mitigate CVE-2026-92024

Immediate Actions Required

Update Firefox to version 156 or the appropriate ESR release (115.41, 140.16, or 153.3) on all endpoints.
Update Thunderbird to version 156, 140.16, or 153.3 depending on the deployed channel.
Prioritize deployment on systems where users regularly render untrusted web content or HTML email.

Patch Information

Mozilla shipped fixes for CVE-2026-92024 across the Firefox and Thunderbird product lines. Fixed builds are Firefox 156, Firefox ESR 115.41, Firefox ESR 140.16, Firefox ESR 153.3, Thunderbird 156, Thunderbird 140.16, and Thunderbird 153.3. Details are provided in Mozilla Security Advisory MFSA-2026-92, MFSA-2026-93, MFSA-2026-94, MFSA-2026-95, and MFSA-2026-96.

Workarounds

Configure Thunderbird to display messages as plain text to suppress SVG rendering in email content until patches are applied.
Restrict navigation to untrusted sites through DNS filtering, proxy allow-lists, or browser policies while updates are staged.
Block or strip .svg attachments at the email gateway for user populations that cannot be patched immediately.