CVE-2026-100824: Firefox Places Privilege Escalation Flaw

CVE-2026-100824 Overview

CVE-2026-100824 is a privilege escalation vulnerability in the Places component used by Mozilla Firefox and Thunderbird. The Places component manages bookmarks, history, and tagging data within Mozilla applications. An attacker can leverage this flaw over the network with user interaction to escalate privileges within the affected browser or mail client. Mozilla addressed the issue in Firefox 157, Firefox ESR 153.4, Thunderbird 157, and Thunderbird 153.4. The vulnerability is classified under [CWE-269] Improper Privilege Management.

Critical Impact
Successful exploitation allows an attacker to gain elevated privileges within the browser or mail client context, leading to compromise of confidentiality, integrity, and availability.

Affected Products

Mozilla Firefox versions prior to 157
Mozilla Firefox ESR versions prior to 153.4
Mozilla Thunderbird versions prior to 157 and prior to 153.4

Discovery Timeline

2026-09-29 - CVE-2026-100824 published to NVD
2026-09-30 - Last updated in NVD database

Technical Details for CVE-2026-100824

Vulnerability Analysis

The vulnerability resides in the Places component, which handles browser history, bookmarks, tags, and related metadata storage in Mozilla applications. Improper privilege management within this component allows an attacker to perform actions with elevated rights that should be restricted to the browser or a trusted context. Because Places is invoked during routine browsing and mail operations, the attack surface is broad across both Firefox and Thunderbird.

Mozilla published the fix across multiple advisories, including MFSA-2026-97, MFSA-2026-100, MFSA-2026-101, and MFSA-2026-103. Tracking details are available in Mozilla Bug Report #2054767.

Root Cause

The root cause is classified as Improper Privilege Management [CWE-269] within the Places subsystem. Code paths in Places do not correctly enforce privilege boundaries, allowing untrusted content to trigger operations that should be limited to privileged callers. Mozilla has not disclosed further technical specifics pending patch adoption.

Attack Vector

Exploitation requires network delivery and user interaction, consistent with a web-based or content-driven attack. A user must load attacker-controlled content in Firefox or open crafted content in Thunderbird for the exploit to trigger. Once triggered, the attacker gains privileges beyond those normally granted to web or mail content. No verified proof-of-concept is publicly available at the time of writing. Refer to the Mozilla advisories for authoritative technical details.

Detection Methods for CVE-2026-100824

Indicators of Compromise

Unexpected modifications to the Places SQLite database files (places.sqlite, places.sqlite-wal) outside of normal browsing activity.
Firefox or Thunderbird processes spawning unexpected child processes or writing to protected profile directories.
Outbound connections from browser or mail client processes to unfamiliar domains immediately following user-initiated content loads.

Detection Strategies

Inventory Firefox, Firefox ESR, and Thunderbird installations and flag hosts running versions below the patched releases.
Monitor endpoint telemetry for anomalous behavior originating from firefox.exe, thunderbird.exe, or their Linux and macOS equivalents.
Correlate browser process behavior with proxy and DNS logs to identify suspicious content deliveries preceding privilege changes.

Monitoring Recommendations

Enable process-tree and file-write telemetry on user endpoints and mail servers running Thunderbird.
Alert on modifications to browser profile directories by non-browser processes.
Track advisory pages MFSA-2026-97 and related MFSAs for updated indicators.

How to Mitigate CVE-2026-100824

Immediate Actions Required

Upgrade Firefox to version 157 and Firefox ESR to 153.4 across all managed endpoints.
Upgrade Thunderbird to version 157 or 153.4 on all workstations and mail-processing hosts.
Restart affected applications after patching to ensure the vulnerable Places component is unloaded from memory.

Patch Information

Mozilla shipped fixes in Firefox 157, Firefox ESR 153.4, Thunderbird 157, and Thunderbird 153.4. Administrators should consult MFSA-2026-97, MFSA-2026-100, MFSA-2026-101, and MFSA-2026-103 for release-specific details and download links.

Workarounds

No vendor-supplied workaround exists; patching is the only supported remediation path.
Reduce exposure by restricting untrusted browsing and blocking attachments and remote content in Thunderbird where feasible.
Enforce least-privilege user accounts to limit the impact of any successful browser-level privilege escalation.

bash

# Configuration example: verify installed Firefox version on Linux endpoints
firefox --version

# Verify Thunderbird version
thunderbird --version