CVE-2016-5260 in Firefox
Summary
by MITRE
Mozilla Firefox before 48.0 mishandles changes from INPUT type="password" to INPUT type="text" within a single Session Manager session, which might allow attackers to discover cleartext passwords by reading a session restoration file.
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Analysis
by VulDB Data Team • 03/16/2019
This vulnerability exists in Mozilla Firefox versions prior to 48.0 and relates to improper handling of input field type changes within session manager functionality. The flaw occurs when a user switches an input field from type="password" to type="text" during a browsing session, creating a scenario where session restoration data retains sensitive information in cleartext format. The vulnerability stems from Firefox's session manager not properly sanitizing or clearing password field contents when the field type changes, allowing potentially sensitive data to persist in session restoration files that are typically stored in plain text format on the filesystem.
The technical implementation of this vulnerability involves the session manager's storage mechanism which preserves form data including input field values across browser sessions. When an INPUT element changes from password to text type, the underlying session restoration code fails to properly invalidate or clear the cached password value, resulting in cleartext password data being written to session restore files. This represents a direct violation of secure data handling principles and demonstrates inadequate input sanitization within the browser's session management subsystem. The vulnerability is particularly concerning because session restore files are often stored in locations accessible to local users and may persist even after browser shutdown, creating opportunities for unauthorized information disclosure.
The operational impact of this vulnerability extends beyond simple information disclosure to potentially enable credential harvesting attacks. Attackers who gain access to a victim's session restore files can extract cleartext passwords that were previously masked in password fields, effectively bypassing the fundamental security mechanism designed to protect sensitive authentication data. This vulnerability aligns with CWE-200 (Information Exposure) and CWE-312 (Cleartext Storage of Sensitive Information) classifications, as it exposes sensitive data through improper storage mechanisms. The attack vector requires local file system access to the session restore files, making it a low-privilege information disclosure vulnerability that can be exploited by malicious local users or malware with file system access. This weakness specifically maps to ATT&CK technique T1005 (Data from Local System) and T1059 (Command and Scripting Interpreter) when combined with other exploitation vectors.
Mitigation strategies for this vulnerability include upgrading to Firefox version 48.0 or later where the issue has been resolved through improved session manager sanitization routines. Administrators should also implement proper file system permissions on session restore directories to limit access to authorized users only. Additional protective measures include disabling session restoration features for sensitive browsing sessions, implementing regular cleanup of session restore files, and monitoring for unauthorized access to browser data directories. The fix implemented by Mozilla involved enhancing the session manager's handling of input field type changes to ensure that password field contents are properly cleared when field types are modified, preventing the persistence of cleartext credentials in session restoration data. Organizations should also consider implementing browser hardening policies that restrict session management functionality in high-security environments where credential exposure risks are particularly concerning.