External risk intelligence

Integer Overflow in Firefox and Thunderbird Graphics Component

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-74964

The vulnerability exists within the Graphics component of web browsers and email clients. These are client-side applications that process untrusted content locally. They are not designed to be public-internet-facing servers or edge services, and their attack surface is restricted to the execution context of the user's local machine.

Integer Overflow

Mozilla Firefox

before 140.14.0141.0.0 to before 153.1.0141.0 to before 153.1.0

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

An integer overflow vulnerability has been identified in the Graphics component of Mozilla products. This issue could potentially allow for significant compromise of confidentiality, integrity, and availability. The main concern is confirming if your organization utilizes the affected software, as the impact would depend on that exposure.

A code flaw in graphics processing.
It affects widely used browsers and email clients.
Confirm relevance and assess potential exposure.

Attack Path

How an attacker could exploit the issue

An attacker could reach this vulnerability through the network by sending specially crafted data to the Graphics component of an affected application. This could allow an attacker to potentially execute arbitrary code, leading to a full compromise of the system. The exact steps to trigger this vulnerability and the specific impact are not detailed in the provided context.

No specific entry conditions are detailed.
Vulnerability triggered by crafted network data.
Risk of code execution and system compromise.

Live Threat

Current exploitation, exposure, and threat context

An integer overflow in the Graphics component could allow an attacker to compromise the application. This vulnerability may affect the integrity and availability of the application and could lead to a complete system compromise when exploited.

Application integrity and availability at risk.
Remote attackers could exploit via crafted content.
Complete application or system compromise possible.

Operational Fix

Recommended remediation, mitigation, and detection steps

In a real-world scenario, application owners and potentially platform teams are responsible for addressing this vulnerability in affected Firefox and Thunderbird deployments. The initial practical step is to identify all instances of the affected software, determine their business criticality and network exposure, and then coordinate with the appropriate teams for remediation.

Application owners should manage remediation efforts.
Verify software deployment and network reachability.
Plan for vendor-coordinated updates.

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 Graphics component in Firefox and Thunderbird?

The Graphics component is a core part of Mozilla Firefox and Thunderbird responsible for rendering web pages, images, and visual interface elements. It acts as a translator between complex data streams and what you see on your screen. Because it frequently processes diverse and complex digital content, it is a critical subsystem for both browser performance and the rendering of rich HTML emails in Thunderbird.

What does an integer overflow mean in the context of CVE-2026-74964?

An integer overflow (CWE-190) occurs when a program tries to store a number too large for the allocated memory space, causing the value to wrap around to an incorrect, often small, number. In CVE-2026-74964, this flaw affects how the Graphics component calculates memory needs. This miscalculation can corrupt memory operations, potentially allowing the application to behave unpredictably or execute unauthorized code.

How does an attacker trigger this Graphics component vulnerability?

The vulnerability is triggered by providing the browser or email client with specially crafted data designed to force an overflow during graphics processing. Note that simply browsing the web or opening emails does not inherently trigger the bug; the data must be specifically engineered to exploit the integer calculation flaw. Without this malicious, malformed content, the component functions as expected.

Why does Halo Surface Signal consider this vulnerability a lower priority?

Halo Surface Signal notes that Firefox and Thunderbird are client-side applications meant for local processing, not public-facing servers. Because the attack surface is restricted to the local user's machine, it is not a traditional internet-exposed service. While the flaw is critical in severity, its reach is limited by the local execution context of the user's software rather than being reachable via standard network service probing.

How should I respond if I use affected versions of Firefox or Thunderbird?

Your first step is to inventory your systems to locate all installed instances of these applications. Once identified, prioritize updating these installations to the patched versions—such as Firefox 154 or Thunderbird 154—provided by Mozilla. Coordinate these updates through your standard software management processes to ensure the security flaw is remediated across all business devices.

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.