CVE-2026-6770 Overview
CVE-2026-6770 is an information disclosure vulnerability (CWE-200) affecting the Storage: IndexedDB component in Mozilla Firefox and Thunderbird. The flaw was addressed in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. An attacker can exploit the issue over the network without authentication or user interaction. Successful exploitation results in limited exposure of confidential data and limited impact to availability. Mozilla published the fix across four security advisories: MFSA-2026-30, MFSA-2026-32, MFSA-2026-33, and MFSA-2026-34.
Critical Impact
Remote attackers can trigger information disclosure through the IndexedDB storage subsystem without requiring credentials or user interaction.
Affected Products
- Mozilla Firefox versions prior to 150
- Mozilla Firefox ESR versions prior to 140.10
- Mozilla Thunderbird versions prior to 150 and prior to 140.10
Discovery Timeline
- 2026-04-21 - CVE-2026-6770 published to NVD
- 2026-04-22 - Last updated in NVD database
Technical Details for CVE-2026-6770
Vulnerability Analysis
The vulnerability resides in the Storage: IndexedDB component used by Mozilla Firefox and Thunderbird. IndexedDB is a transactional, client-side database that web content uses to store structured data within the browser profile. The flaw is classified under CWE-200, Exposure of Sensitive Information to an Unauthorized Actor.
Mozilla categorized this issue as an "Other" defect rather than a memory corruption or code execution bug. The CVSS impact profile indicates partial confidentiality loss and partial availability impact, with no integrity impact. This pattern is consistent with origin or boundary handling errors that allow one web origin to observe data or metadata associated with another.
Thunderbird is affected because it shares the underlying Gecko platform with Firefox. Remote content rendered within the mail client inherits the same exposure surface as the browser engine.
Root Cause
The root cause has not been disclosed in detail by Mozilla. The corresponding bug tracker entry, Mozilla Bug Report #2024220, remains the authoritative source for technical specifics. Mozilla typically restricts access to security-sensitive bug reports until a sufficient patch adoption window has passed.
Attack Vector
Exploitation requires the victim to load attacker-controlled web content in a vulnerable Firefox or Thunderbird build. Because the attack vector is Network and no privileges or user interaction are required beyond visiting a page, a malicious site or a crafted HTML email rendered with remote content enabled can trigger the condition. The attacker gains limited read access to information that should remain isolated by the same-origin policy or the storage partitioning model.
No public proof-of-concept code is available. No verified exploitation in the wild has been reported, and the CVE is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-6770
Indicators of Compromise
- No file-based or network-based indicators of compromise have been published for CVE-2026-6770.
- Endpoints running Firefox builds older than 150, Firefox ESR builds older than 140.10, or Thunderbird builds older than 140.10 or 150 should be treated as exposed assets.
Detection Strategies
- Inventory installed Firefox and Thunderbird versions across managed endpoints and compare against the fixed releases listed in the Mozilla advisories.
- Monitor browser telemetry and proxy logs for sustained outbound connections from Firefox or Thunderbird processes to low-reputation domains hosting active web content.
- Correlate Thunderbird process activity with rendering of remote HTML content, since email is a viable delivery channel for malicious pages.
Monitoring Recommendations
- Track Mozilla advisories MFSA-2026-30 through MFSA-2026-34 for any updates on related issues bundled into the same release.
- Enable browser update auditing in endpoint management platforms to confirm the patched build is deployed.
- Review IndexedDB storage usage policies on sensitive web applications and reduce the volume of confidential data persisted client-side where feasible.
How to Mitigate CVE-2026-6770
Immediate Actions Required
- Upgrade Firefox to version 150 or later on all managed workstations.
- Upgrade Firefox ESR deployments to version 140.10 or later.
- Upgrade Thunderbird to version 150 or to ESR 140.10, depending on the deployed channel.
- Restart browser and mail client processes after the update to ensure the patched binaries are loaded.
Patch Information
Mozilla released fixes in Firefox 150, Firefox ESR 140.10, Thunderbird 150, and Thunderbird 140.10. The patches are documented in MFSA-2026-30, MFSA-2026-32, MFSA-2026-33, and MFSA-2026-34. Administrators should rely on the vendor's automatic update channel where policy permits, or push the corresponding MSI, PKG, or distribution package through their software deployment tooling.
Workarounds
- Disable remote content rendering in Thunderbird for untrusted senders to reduce exposure of the IndexedDB code path through email.
- Restrict browsing to trusted origins through web filtering until the patched Firefox build is fully deployed.
- Consider enforcing strict storage partitioning and disabling third-party storage access where the deployed Firefox version exposes the relevant policy controls.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
