CVE-2025-3032 in Thunderbird
Summary
by MITRE • 04/01/2025
Leaking of file descriptors from the fork server to web content processes could allow for privilege escalation attacks. This vulnerability was fixed in Firefox 137 and Thunderbird 137.
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Analysis
by VulDB Data Team • 04/15/2026
This vulnerability represents a critical privilege escalation flaw in Mozilla Firefox and Thunderbird applications that stems from improper handling of file descriptor inheritance across process boundaries. The issue occurs within the fork server mechanism that manages child processes for web content execution, where file descriptors intended for internal system operations are inadvertently exposed to web content processes that should operate with restricted permissions. This leakage creates a pathway for malicious web content to gain access to sensitive system resources that should remain isolated from untrusted code execution environments.
The technical root cause of CVE-2025-3032 lies in the improper implementation of process isolation mechanisms during the forking operation. When Firefox or Thunderbird creates child processes for web content rendering, the fork server fails to properly close or reset file descriptor handles that are typically reserved for system-level operations. These exposed file descriptors can include handles to system files, network sockets, or other privileged resources that should not be accessible to web-based code running in sandboxed environments. The vulnerability specifically affects the inter-process communication patterns where the parent process maintains certain file handles that are inherited by child processes without proper sanitization.
From an operational impact perspective, this vulnerability enables attackers to perform privilege escalation attacks by leveraging the leaked file descriptors to access system resources that would normally be restricted. An attacker could potentially use these exposed handles to read sensitive system files, manipulate network connections, or gain access to other privileged operations that should remain protected from web content execution. The attack surface is particularly concerning because web content processes typically operate with reduced privileges, but the file descriptor leakage effectively provides malicious code with elevated access rights that bypass normal security boundaries. This vulnerability directly impacts the browser's security model and undermines the isolation mechanisms designed to protect users from malicious web content.
The mitigation for CVE-2025-3032 involves updating to Firefox version 137 or Thunderbird version 137, which contain patches that properly implement file descriptor sanitization during process forking operations. These updates ensure that the fork server correctly closes or resets file descriptor handles before creating child processes, preventing the inheritance of privileged handles by web content processes. Organizations should prioritize immediate deployment of these security updates across all affected systems, as the vulnerability represents a significant risk to user security. Additionally, security teams should monitor for any potential exploitation attempts and consider implementing additional process monitoring to detect unauthorized file descriptor access patterns that might indicate exploitation attempts.
This vulnerability aligns with CWE-362, which describes concurrent access conditions that lead to race conditions, and specifically relates to improper file descriptor handling in process management. The issue also maps to ATT&CK technique T1059.007 for command and scripting interpreter, where attackers might leverage the elevated privileges gained through file descriptor leakage to execute malicious code with higher privileges. The security implications extend beyond simple privilege escalation to potentially enable more sophisticated attacks that exploit the compromised process isolation boundaries.