CVE-2026-109731 Mozilla CVE debrief

Who should care

Defenders responsible for managing Mozilla Firefox deployments should assess exposure and apply patches as necessary. This includes reviewing and updating inventory of Firefox deployments to ensure they are up-to-date and monitoring for potential exploitation attempts to detect possible security breaches. Defenders should also verify Firefox version and apply patches if necessary, and review compensating controls for exposed systems while remediation is

Why it matters

CVE-2026-109731 is a vulnerability in the Graphics: Canvas2D component of Mozilla Firefox. Defenders should verify exposure in their Firefox deployments and apply available patches to prevent potential security issues.

• Verify and apply patches to prevent potential security issues
• Review and update inventory of Firefox deployments to ensure they are up-to-date
• Monitor for potential exploitation attempts to detect possible security breaches

Technical summary

The Graphics: Canvas2D component in Mozilla Firefox has incorrect boundary conditions, which could potentially lead to security issues. This vulnerability was fixed in Firefox 158 and Firefox ESR 153.5. The incorrect boundary conditions may allow attackers to exploit the vulnerability, potentially leading to security breaches. Defenders should prioritize verifying exposure in their Firefox deployments and applying the available patches to prevent potential security issues. The vulnerability affects the Graphics: Canvas2D component, and defenders should review their deployments to ensure they are up-to-date.

Defensive priority

Defenders should prioritize verifying exposure in their Firefox deployments and applying the available patches.

Recommended defensive actions

• Verify Firefox version and apply patches if necessary
• Review and update inventory of Firefox deployments
• Monitor for potential exploitation attempts
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and associated source item provide details on the vulnerability, which was fixed in Firefox 158 and Firefox ESR 153.5. The vulnerability affects the Graphics: Canvas2D component of Mozilla Firefox. Defenders should verify exposure in their Firefox deployments and apply available patches to prevent potential security issues. The source item provides vulnerability details, and defenders should review this information to understand the potential impact on their systems.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.