CVE-2025-3035: Firefox Information Disclosure Vulnerability

CVE-2025-3035 Overview

CVE-2025-3035 is an information disclosure vulnerability in Mozilla Firefox affecting the browser's built-in AI chatbot feature. When a user activates the AI chatbot in one tab and later activates it in another tab, the document title from the previous tab leaks into the chat prompt of the new session. This exposes potentially sensitive browsing context to the AI chatbot provider or any observer of the chat prompt content. Mozilla addressed the issue in Firefox 137 and tracked it under Mozilla Security Advisory MFSA-2025-20. The weakness is classified as [CWE-359] Exposure of Private Personal Information to an Unauthorized Actor.

Critical Impact
Document titles from previously visited tabs, which may contain sensitive keywords, account identifiers, or private page context, can be transmitted to AI chatbot providers without user awareness.

Affected Products

Mozilla Firefox versions prior to 137
Firefox builds with the integrated AI chatbot sidebar feature enabled
Desktop platforms (Windows, macOS, Linux) shipping the affected chatbot integration

Discovery Timeline

2025-04-01 - CVE-2025-3035 published to the National Vulnerability Database (NVD)
2025-04-01 - Mozilla publishes Mozilla Security Advisory MFSA-2025-20 with Firefox 137 patch
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-3035

Vulnerability Analysis

The vulnerability resides in the AI chatbot integration introduced into recent Firefox releases. Firefox exposes a sidebar chatbot that can receive contextual data from the active tab, including the page title, selected text, and URL. The tab-switching logic responsible for updating chatbot context fails to properly clear or replace the previously captured document title when the chatbot is activated in a different tab. As a result, the stale title from the earlier tab is bundled into the prompt sent to the AI chatbot provider. The issue is a state management flaw in the chatbot context propagation code, not a memory safety bug. Additional technical details are tracked in Mozilla Bugzilla Report #1952268.

Root Cause

The root cause is improper reinitialization of the chatbot's tab context state. When the user activates the chatbot in a subsequent tab, the code path reuses the previous tab's document title reference instead of fetching the current tab's title. This creates a cross-context data leak between browsing sessions within the same browser profile.

Attack Vector

Exploitation requires no authentication and can be triggered remotely by an attacker who controls or observes the AI chatbot endpoint. The attack surface is limited to users who actively use the Firefox AI chatbot across multiple tabs. Document titles frequently contain sensitive identifiers such as email subjects, banking account labels, internal application page names, or search queries, all of which could leak to the AI provider.

No public proof-of-concept exploit is available. The vulnerability mechanism is documented in the referenced Mozilla Bugzilla report and does not require synthetic code to explain, as it stems from a stale-state reuse condition in the browser's chatbot context handler.

Detection Methods for CVE-2025-3035

Indicators of Compromise

Firefox builds reporting a version number lower than 137 in about:support or the User-Agent header
Outbound network requests to configured AI chatbot providers containing document titles that do not match the currently active tab
Browser telemetry showing chatbot activation events across multiple tabs within a single session

Detection Strategies

Inventory Firefox versions across managed endpoints and flag any installation below 137 for remediation
Inspect HTTP request payloads to AI chatbot endpoints in proxy or DLP logs for unexpected title strings
Correlate chatbot usage telemetry with tab-switch events to identify sessions vulnerable to the leak

Monitoring Recommendations

Monitor endpoint software inventory for Firefox versions and alert on outdated installations
Log and review egress traffic to third-party AI provider domains from browsers
Track user-reported anomalies where chatbot responses reference content from unrelated tabs

How to Mitigate CVE-2025-3035

Immediate Actions Required

Update all Firefox installations to version 137 or later using Mozilla's official update channels
Verify update deployment across managed endpoints and confirm the reported version in about:support
Communicate the risk to users who rely on the AI chatbot sidebar for handling sensitive content

Patch Information

Mozilla fixed CVE-2025-3035 in Firefox 137. Refer to Mozilla Security Advisory MFSA-2025-20 for the complete list of security fixes bundled in the release. Enterprise administrators using Firefox ESR should confirm that their ESR channel has received the corresponding backported fix.

Workarounds

Disable the Firefox AI chatbot sidebar via the browser.ml.chat.enabled preference in about:config until patching is complete
Restrict outbound network access to AI chatbot provider domains using enterprise proxy or firewall rules
Instruct users to avoid activating the chatbot across multiple tabs containing sensitive content on unpatched browsers

bash

# Configuration example: disable Firefox AI chatbot via enterprise policy (policies.json)
{
  "policies": {
    "Preferences": {
      "browser.ml.chat.enabled": {
        "Value": false,
        "Status": "locked"
      }
    }
  }
}