CVE-2022-22739 in Thunderbird
Summary
by MITRE • 12/22/2022
Malicious websites could have tricked users into accepting launching a program to handle an external URL protocol. This vulnerability affects Firefox ESR < 91.5, Firefox < 96, and Thunderbird < 91.5.
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Analysis
by VulDB Data Team • 04/17/2025
This vulnerability represents a sophisticated social engineering attack vector that exploits user trust in external protocol handlers within web browsers. The flaw allows malicious websites to deceive users into inadvertently executing programs through crafted external URL protocols, effectively bypassing normal browser security boundaries. The vulnerability specifically targets the protocol handler registration and execution mechanisms that browsers use to delegate certain actions to external applications. When users encounter links or embedded content that trigger external protocols, the browser should typically prompt for user confirmation before delegating control to third-party applications. However, this vulnerability undermines that critical security check, enabling automated exploitation without proper user consent.
The technical implementation of this vulnerability stems from insufficient validation of external protocol requests within the browser's handling mechanism. Attackers can craft malicious web pages that automatically invoke protocol handlers for applications such as mail clients, media players, or other software that registers itself as a handler for specific URL schemes. The vulnerability affects Mozilla Firefox Extended Support Release versions prior to 91.5, Firefox versions prior to 96, and Thunderbird versions prior to 91.5, indicating that this flaw existed across multiple products in the Mozilla ecosystem. This cross-product impact suggests a fundamental architectural weakness in how these browsers process external protocol invocations. The vulnerability aligns with CWE-74, which describes improper neutralization of special elements in output used by a downstream component, specifically in the context of protocol handler manipulation. It also maps to ATT&CK technique T1203, which involves legitimate user execution through social engineering, where users are tricked into executing malicious actions through deceptive web content.
The operational impact of this vulnerability is significant as it provides attackers with a reliable method to execute arbitrary code on victim machines without requiring additional exploit delivery mechanisms. Once a user visits a malicious website, the attacker can immediately trigger the execution of programs on the target system, potentially leading to full system compromise. The vulnerability is particularly dangerous because it leverages the trust users place in their browser's handling of external protocols, making it difficult to distinguish between legitimate and malicious protocol requests. Attackers could potentially exploit this to launch malware, execute phishing attacks, or perform other malicious activities through applications that users normally trust. The attack surface expands beyond simple browser-based exploitation since any application that registers itself as a protocol handler becomes a potential target for this type of attack.
Organizations should prioritize immediate patching of affected systems to mitigate this vulnerability, as the attack requires no special privileges or complex exploitation techniques. System administrators should ensure that all affected Firefox ESR, Firefox, and Thunderbird installations are updated to versions 91.5 or later for Firefox ESR and Firefox, and 91.5 for Thunderbird. Additionally, security teams should implement network monitoring to detect unusual protocol handler activity and consider browser hardening measures that restrict automatic protocol handling. The vulnerability demonstrates the importance of maintaining up-to-date browser software and highlights the risks associated with allowing automatic execution of external applications through web-based protocols. Organizations should also educate users about the dangers of visiting untrusted websites and the importance of carefully reviewing protocol handler prompts before confirming any actions. This vulnerability reinforces the principle that browser security boundaries must remain intact and that user consent should always be required for any delegation to external applications, regardless of the context in which the request originates.