CVE-2026-6783: Mozilla Firefox Buffer Overflow Vulnerability

CVE-2026-6783 Overview

CVE-2026-6783 is an integer overflow vulnerability affecting the Audio/Video Playback component in Mozilla Firefox and Mozilla Thunderbird. The vulnerability stems from incorrect boundary conditions that can lead to an integer overflow during media processing operations. This flaw was addressed in Firefox 150 and Thunderbird 150.

Critical Impact

Attackers can exploit this integer overflow vulnerability via network-based attacks to potentially compromise data integrity in affected Mozilla applications.

Affected Products

• Mozilla Firefox (versions prior to 150)
• Mozilla Thunderbird (versions prior to 150)

Discovery Timeline

• 2026-04-21 - CVE-2026-6783 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6783

Vulnerability Analysis

This vulnerability is classified as CWE-190 (Integer Overflow or Wraparound). The flaw exists within the Audio/Video Playback component of Mozilla products, where improper boundary validation can trigger an integer overflow condition. When processing specially crafted media content, the component fails to properly validate numeric boundaries, allowing arithmetic operations to exceed the maximum value that can be stored in an integer variable, causing the value to wrap around to an unexpected value.

The vulnerability is exploitable remotely without requiring user interaction or authentication, making it accessible to attackers over the network. When successfully exploited, the integer overflow can lead to integrity impacts, potentially allowing manipulation of data or application behavior during media playback operations.

Root Cause

The root cause of this vulnerability lies in insufficient boundary checking within the Audio/Video Playback component. When the component processes media file parameters such as frame dimensions, buffer sizes, or timing calculations, it performs arithmetic operations without adequate validation that the results will remain within valid integer bounds. This oversight allows attackers to craft malicious media files with parameters designed to trigger integer overflow conditions during playback processing.

Attack Vector

The attack vector for CVE-2026-6783 is network-based. An attacker can exploit this vulnerability by hosting or delivering a specially crafted audio or video file to a victim. When a user attempts to play the malicious media content in Firefox or opens an email containing such content in Thunderbird, the integer overflow is triggered in the playback component.

The vulnerability does not require any special privileges or user interaction beyond normal browsing or email activities, making it relatively straightforward for attackers to exploit in real-world scenarios. However, the impact is limited to integrity concerns, and there is no evidence of active exploitation in the wild.

The vulnerability mechanism involves manipulating media container or codec parameters to cause integer arithmetic in the playback component to exceed safe bounds. When the overflow occurs, subsequent memory operations or buffer calculations may use incorrect values, potentially leading to unexpected application behavior. For detailed technical information, refer to Mozilla Bug Report #2027564.

Detection Methods for CVE-2026-6783

Indicators of Compromise

• Abnormal crashes or unexpected behavior in Firefox or Thunderbird during media playback
• Browser process consuming unusual amounts of memory when loading audio/video content
• Presence of unusual media files with malformed headers or atypical parameter values
• Log entries indicating media decoding errors or boundary violations

Detection Strategies

• Monitor for crashes or stability issues in Firefox and Thunderbird related to media playback functions
• Implement network traffic analysis to identify potentially malicious media files being delivered to endpoints
• Deploy endpoint detection rules that flag unusual behavior patterns during audio/video processing
• Review application logs for repeated media parsing errors or component failures

Monitoring Recommendations

• Enable crash reporting in Firefox and Thunderbird to capture and analyze any stability issues related to media playback
• Utilize SentinelOne's behavioral AI to detect anomalous process behavior when media files are opened
• Monitor for network requests to known malicious domains serving crafted media content
• Configure endpoint protection to alert on integrity violations in browser processes

How to Mitigate CVE-2026-6783

Immediate Actions Required

• Update Mozilla Firefox to version 150 or later immediately
• Update Mozilla Thunderbird to version 150 or later immediately
• Review and restrict access to untrusted media content sources
• Consider disabling automatic media playback until patches are applied

Patch Information

Mozilla has released security patches addressing this vulnerability. Users and administrators should update to the fixed versions as documented in the official Mozilla Security Advisories:

• Mozilla Security Advisory MFSA-2026-30 - Firefox 150 security update
• Mozilla Security Advisory MFSA-2026-33 - Thunderbird 150 security update

Organizations using enterprise deployment tools should prioritize pushing these updates to all managed endpoints. The patches correct the boundary condition validation in the Audio/Video Playback component to prevent integer overflow conditions.

Workarounds

• Disable autoplay features in Firefox by navigating to about:config and setting media.autoplay.default to 5 (block all audio and video)
• Configure email clients to not automatically load or preview media attachments
• Implement network-level filtering to block potentially malicious media file types from untrusted sources
• Use browser extensions that block media content from unknown or untrusted domains until patches can be applied

# Firefox configuration to disable media autoplay
# In about:config, set:
# media.autoplay.default = 5
# media.autoplay.blocking_policy = 2

# For enterprise deployments, use policies.json:
# {
#   "policies": {
#     "Preferences": {
#       "media.autoplay.default": 5,
#       "media.autoplay.blocking_policy": 2
#     }
#   }
# }