CVE-2026-2773: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-2773 Overview

CVE-2026-2773 is a memory safety vulnerability in the Web Audio component of Mozilla Firefox and Thunderbird. Incorrect boundary conditions in the component create a buffer overflow condition [CWE-119] that an attacker can trigger remotely without authentication or user interaction. Mozilla addressed the issue in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8.

Critical Impact
Remote attackers can exploit a crafted web page or HTML email to trigger memory corruption in the Web Audio component, potentially leading to arbitrary code execution within the browser process.

Affected Products

Mozilla Firefox (versions prior to 148)
Mozilla Firefox ESR (versions prior to 115.33 and 140.8)
Mozilla Thunderbird (versions prior to 148 and 140.8)

Discovery Timeline

2026-02-24 - CVE-2026-2773 published to NVD
2026-04-13 - Last updated in NVD database

Technical Details for CVE-2026-2773

Vulnerability Analysis

The vulnerability resides in the Web Audio implementation shared by Firefox and Thunderbird. Web Audio provides JavaScript APIs for processing and synthesizing audio inside web content. Incorrect boundary conditions during audio buffer handling allow data to be read or written outside the intended memory region. This class of flaw is tracked under [CWE-119], which covers improper restriction of operations within the bounds of a memory buffer.

An attacker who hosts a malicious web page or sends an HTML email containing crafted audio processing logic can reach the vulnerable code path. Successful exploitation can corrupt browser memory and undermine renderer process isolation. The flaw affects all three supported release trains (mainline, ESR 115, and ESR 140), indicating the defect existed in long-lived shared code.

Root Cause

The root cause is a boundary condition error in audio buffer processing. Length, offset, or index calculations on audio sample data fail to enforce the limits of the underlying memory allocation. When the component operates on attacker-controlled sample counts or channel configurations, the math used to bound reads or writes produces values outside the buffer. Mozilla classified this defect as a memory safety bug warranting backports to all maintained release branches.

Attack Vector

The attack vector is network-based and requires no privileges or user interaction beyond loading attacker-controlled content. In Firefox, an attacker delivers a malicious page that instantiates a Web Audio context and supplies crafted parameters. In Thunderbird, the same primitives are reachable through HTML email rendering when scripting or audio elements are processed. See Mozilla Bug Report #2014832 and Mozilla Security Advisory MFSA-2026-13 for vendor technical detail.

No public proof-of-concept code or verified exploit example is available at this time, so synthetic exploitation code is not included.

Detection Methods for CVE-2026-2773

Indicators of Compromise

Firefox or Thunderbird child processes terminating unexpectedly with access violation or SIGSEGV exit codes after loading specific pages or messages.
Crash reports referencing Web Audio symbols such as AudioBuffer, AudioNodeEngine, or MediaTrackGraph in the stack.
Outbound connections from firefox.exe or thunderbird.exe to previously unseen hosts shortly after a crash event.
Spawning of unexpected child processes (cmd.exe, powershell.exe, shell binaries) from a browser or mail client process tree.

Detection Strategies

Inventory installed Firefox and Thunderbird versions across the fleet and flag any build below the fixed versions (Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, Thunderbird 140.8).
Hunt for browser process crashes correlated with Web Audio usage in telemetry from EDR or crash reporting services.
Monitor for browser processes performing post-exploitation behavior such as writing executables or modifying autostart locations.

Monitoring Recommendations

Forward browser and mail client process events, including child process creation and module loads, to a central data lake for retrospective hunting.
Alert on anomalous network egress originating from renderer or content processes.
Track Mozilla advisories MFSA-2026-13 through MFSA-2026-17 for related fixes shipped in the same release cycle.

How to Mitigate CVE-2026-2773

Immediate Actions Required

Update Firefox to version 148 or later on all managed endpoints.
Update Firefox ESR deployments to 115.33 or 140.8, depending on the supported branch in use.
Update Thunderbird to 148 or 140.8 across user and server-managed installations.
Restart browser and mail client processes after deployment to ensure the patched binaries are loaded.

Patch Information

Mozilla fixed the issue in Firefox 148, Firefox ESR 115.33, Firefox ESR 140.8, Thunderbird 148, and Thunderbird 140.8. Refer to Mozilla Security Advisory MFSA-2026-13, MFSA-2026-14, MFSA-2026-15, MFSA-2026-16, and MFSA-2026-17 for branch-specific patch metadata.

Workarounds

Disable JavaScript on untrusted sites using a content policy or extension until patches are deployed.
In Thunderbird, configure the mail client to render messages as plain text to avoid HTML and embedded media processing.
Restrict outbound network access for browser and mail client processes through host firewall policy to limit post-exploitation impact.

bash

# Configuration example: enforce plain-text message display in Thunderbird
# Set the following preferences in prefs.js or via enterprise policy
user_pref("mailnews.display.prefer_plaintext", true);
user_pref("mailnews.display.html_as", 1);
user_pref("mailnews.display.disallow_mime_handlers", 3);