CVE-2026-6782: Mozilla Firefox Information Disclosure Flaw

CVE-2026-6782 Overview

CVE-2026-6782 is an information disclosure vulnerability affecting the IP Protection component in Mozilla Firefox and Mozilla Thunderbird. Remote attackers can exploit this flaw over the network without authentication or user interaction. The weakness is classified under [CWE-200] (Exposure of Sensitive Information to an Unauthorized Actor). Mozilla addressed the issue in Firefox 150 and Thunderbird 150, as documented in advisories MFSA-2026-30 and MFSA-2026-33. The bug compromises the confidentiality guarantees of the IP Protection feature, which is designed to mask client network identifiers from remote endpoints.

Critical Impact

Remote attackers can bypass IP Protection in Firefox and Thunderbird to obtain sensitive network identifiers without user interaction, undermining the privacy assurances the feature provides to users.

Affected Products

• Mozilla Firefox versions prior to 150
• Mozilla Thunderbird versions prior to 150
• Clients relying on the IP Protection component for network privacy

Discovery Timeline

• 2026-04-21 - CVE-2026-6782 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6782

Vulnerability Analysis

The vulnerability resides in the IP Protection component shared by Firefox and Thunderbird. IP Protection is intended to conceal a user's originating IP address and related metadata when communicating with remote services. The flaw permits a remote actor to obtain information that the component is supposed to shield. Because the attack occurs over the network with no privileges and no user interaction, exploitation can be triggered by serving malicious content or initiating crafted network exchanges with a vulnerable client. The impact is limited to confidentiality, with no direct effect on integrity or availability of the host system.

Root Cause

Mozilla's advisory identifies the defect as an information disclosure within the IP Protection component, mapped to [CWE-200]. The component fails to enforce the boundary between data that should remain private to the client and data emitted to remote peers. Technical specifics are tracked in Mozilla Bug Report #2026571.

Attack Vector

The attack vector is network-based. An attacker hosts or controls a remote endpoint that a vulnerable Firefox or Thunderbird client contacts. During the exchange, the IP Protection component leaks information the user expected to remain protected. No authentication, privileges, or user clicks are required beyond normal browsing or mail retrieval.

No public proof-of-concept exploit code is available for this issue. Refer to the Mozilla Security Advisory MFSA-2026-30 and Mozilla Security Advisory MFSA-2026-33 for vendor-supplied technical context.

Detection Methods for CVE-2026-6782

Indicators of Compromise

• Firefox or Thunderbird clients running versions earlier than 150 generating outbound connections while IP Protection is enabled.
• Unexpected disclosure of client network identifiers to remote services that should have received only proxied or masked metadata.
• Endpoint inventories reporting mozilla:firefox or mozilla:thunderbird builds prior to 150 in production environments.

Detection Strategies

• Inventory all Firefox and Thunderbird installations and compare installed versions against the fixed baseline of 150.
• Correlate process and version telemetry from managed endpoints with the affected CPE entries cpe:2.3:a:mozilla:firefox and cpe:2.3:a:mozilla:thunderbird.
• Review network egress logs for sessions where IP Protection should have been active but origin metadata appears in plaintext.

Monitoring Recommendations

• Alert on outdated Mozilla browser or mail client versions detected on managed endpoints.
• Track installation and update events for firefox.exe, firefox-bin, and thunderbird.exe binaries to confirm patch rollout.
• Forward browser and mail client version inventory to a centralized data lake for continuous compliance reporting against this CVE.

How to Mitigate CVE-2026-6782

Immediate Actions Required

• Update Mozilla Firefox to version 150 or later on all managed endpoints.
• Update Mozilla Thunderbird to version 150 or later, including extended support builds where applicable.
• Restart browser and mail client processes after the upgrade to ensure the patched IP Protection component is loaded.

Patch Information

Mozilla released fixes in Firefox 150 and Thunderbird 150. Patch details are documented in Mozilla Security Advisory MFSA-2026-30 and Mozilla Security Advisory MFSA-2026-33. Administrators using enterprise deployment tooling should distribute the updated MSI, PKG, or repository packages and validate the version string post-deployment.

Workarounds

• Disable the IP Protection feature until clients are updated to a fixed version, accepting reduced privacy in exchange for closing the disclosure path.
• Route Firefox and Thunderbird traffic through a vetted enterprise proxy or VPN that independently masks client network identifiers.
• Restrict use of vulnerable clients on networks where exposure of internal IP metadata would be sensitive.

# Verify installed versions across managed endpoints
firefox --version
thunderbird --version

# Expected output should report 150 or later, for example:
# Mozilla Firefox 150.0
# Thunderbird 150.0