External risk intelligence

Firefox and Thunderbird Storage Quota Manager Sandbox Escape

CVE advisorySeverity: CRITICAL (CVSS 9.6)

CVE-2026-117962

This vulnerability is a sandbox escape within a web browser (Firefox/Thunderbird). Sandbox escapes are client-side issues that require the victim to already be running the application and typically involve processing malicious content. They are not internet-facing services, gateways, or reachable infrastructure components that can be targeted directly from the internet.

Memory Corruption

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This CVE involves a critical flaw in browser technology that could allow an attacker to break out of a protected environment. While the primary concern is confirming relevance and exposure to our specific technology stack, such vulnerabilities can broadly impact user data and system integrity if exploited.

Browser sandbox escape flaw found.
Matters for potential data and system integrity.
Confirm relevance and exposure to our systems.

Attack Path

How an attacker could exploit the issue

An attacker can exploit this vulnerability by tricking a user into visiting a malicious website. When the user interacts with specially crafted content on this site, it can lead to a sandbox escape within the browser. This allows the attacker to break out of the browser's restricted environment, potentially leading to significant compromise of the user's system.

Entry condition: User visits a malicious website.
Trigger point: Interaction with crafted content.
Resulting risk: Sandbox escape and system compromise.

Live Threat

Current exploitation, exposure, and threat context

A sandbox escape in the Storage: Quota Manager component could allow an attacker to break out of the browser's isolated environment. This could potentially impact system data and user data when supported by the advisory's conditions, by enabling a loss of confidentiality, integrity, and availability.

System and user data
Malicious content processing
Loss of confidentiality, integrity, and availability

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability affects the Storage: Quota Manager component within Mozilla Firefox and Thunderbird. Ownership likely resides with the application support team or client endpoint management, as it impacts end-user workstations. The immediate first step is to inventory all deployed instances of the affected software, confirm their reachability and criticality, and identify the accountable owners for remediation planning.

Application owners should prioritize this.
Verify deployed instances and reachability.
Plan remediation based on risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Storage: Quota Manager component in Firefox and Thunderbird?

The Storage: Quota Manager is a background system within Mozilla Firefox and Thunderbird. It manages how much disk space websites or web applications are permitted to use for storing local data, such as cached files or offline site information. It acts as a gatekeeper to ensure no single web service consumes excessive storage, maintaining a balance between browser performance and system resource management.

How does CWE-119 lead to a sandbox escape in CVE-2026-117962?

CWE-119 refers to improper restriction of operations within the bounds of a memory buffer. In this CVE, incorrect boundary conditions in the Quota Manager mean the browser fails to correctly validate the size of data being handled. An attacker can supply specially crafted data that overflows these boundaries, allowing them to break out of the browser's sandbox—a security partition designed to prevent malicious web content from accessing or modifying your underlying computer system.

Do I need to visit a specific site to trigger this vulnerability?

Yes, an attacker generally needs to lure a user into interacting with a malicious website or specially crafted content. It is important to note that simply having the browser installed or running in the background does not trigger this flaw. The exploit relies on the browser's engine actively processing the malicious instructions provided by a site you visit, meaning the vulnerability is inactive if you are not actively browsing untrusted or compromised web pages.

Is my network infrastructure at risk from this CVE?

According to Halo Surface Signal, this vulnerability is very unlikely to be an internet-facing threat to your infrastructure. Because the flaw exists within client-side software like Firefox and Thunderbird, it cannot be targeted directly as a reachable network service. The primary risk is limited to individual user workstations where the software is actively used, rather than your server-side network components or gateways.

What are the first steps to address CVE-2026-117962?

Begin by identifying all systems in your environment that run Firefox or Thunderbird. Once you have a complete inventory, verify which versions are installed across your user workstations. Since the fix is included in newer releases, prioritize updating those instances to the latest versions. Coordinate with your endpoint management or application support teams to ensure these updates are deployed to maintain the integrity of your users' local data.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.