External risk intelligence

Firefox and Thunderbird Audio Video Component Integer Overflow.

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-2774

This vulnerability affects web browsers and email clients (Firefox and Thunderbird). These applications are user-side client software, not network-accessible services, appliances, or infrastructure gateways. Exposure is limited to the end-user's local environment where the software is installed and executed, rather than being a reachable public-facing network surface.

Integer Overflow

Mozilla Firefox

before 115.33.0before 148.0128.0 to before 140.8.0before 140.8.0

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

A critical integer overflow vulnerability has been identified in the Audio/Video component of Mozilla's Firefox and Thunderbird products. This issue could allow for significant compromise of confidentiality, integrity, and availability. While the vulnerability is exploitable over the network, its impact is primarily limited to the end-user's local environment.

Flaw in audio/video handling could be exploited.
Affects widely used Firefox and Thunderbird software.
Confirm relevance and exposure within your environment.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by sending specially crafted audio or video data to a user's application. This could occur over the network without requiring any special privileges or user interaction. Successfully triggering the vulnerability could allow an attacker to gain significant control, impacting confidentiality, integrity, and availability.

No special access required.
Triggered by malformed media data.
High impact on confidentiality, integrity, and availability.

Live Threat

Current exploitation, exposure, and threat context

An integer overflow in the audio and video component of affected Mozilla products could allow an attacker to remotely execute code. This could occur when processing specially crafted media content.

Affects audio/video component.
Remote code execution via crafted media.
System compromise and data theft possible.

Operational Fix

Recommended remediation, mitigation, and detection steps

Application owners and potentially infrastructure or platform teams are likely responsible for addressing this vulnerability in Firefox and Thunderbird. The initial practical step is to identify all instances of these applications, confirm their reachability and business criticality, and then assign ownership for remediation planning based on the assessed risk.

Identify application owners and assets.
Verify reachability and business criticality.
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 Firefox and Thunderbird in this context?

Firefox is a widely used web browser, and Thunderbird is an email client, both developed by Mozilla. These software programs provide the environment for navigating the internet, rendering media content, and managing communications. CVE-2026-2774 specifically affects the internal Audio/Video component responsible for processing various media formats within these applications.

How does an integer overflow impact my software?

This vulnerability is classified as an integer overflow, or CWE-190. In simple terms, the software makes a calculation error while processing audio or video data, resulting in a number that exceeds the space allocated for it. This flaw can confuse the program's logic, potentially allowing an attacker to bypass security measures, steal data, or gain unauthorized control over the application's functions.

Do I need to interact with malicious content to trigger this?

No, this vulnerability does not require any specific user action to be triggered. An attacker can exploit the flaw by sending specially crafted audio or video data to the application. It is important to note that simply having the software installed on a system does not automatically trigger the bug; the application must actively receive and attempt to process the malicious media file.

Is my organization at risk from this CVE?

Halo Surface Signal indicates that because Firefox and Thunderbird are end-user client applications rather than network-accessible servers or infrastructure, the vulnerability is not exposed as a public-facing network service. Risk is concentrated in the local environment of individual users. You should prioritize identifying where these applications are deployed across your organization to assess your overall footprint.

When should I take action for CVE-2026-2774?

You should begin by locating all versions of Firefox and Thunderbird within your environment to determine which are affected. Once identified, assign ownership for update management and plan to migrate those systems to the patched versions—such as Firefox 148 or Thunderbird 148—provided by the vendor. Prioritize updates on machines that frequently access unverified or external media sources.

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.