CVE-2018-5162 in Thunderbird
Summary
by MITRE
Plaintext of decrypted emails can leak through the src attribute of remote images, or links. This vulnerability affects Thunderbird ESR < 52.8 and Thunderbird < 52.8.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability represents a critical information disclosure flaw in Mozilla Thunderbird email clients that allows attackers to potentially extract plaintext content from decrypted emails through maliciously crafted remote image references. The vulnerability specifically impacts Thunderbird ESR versions prior to 52.8 and standard Thunderbird versions before 52.8, making it a significant concern for organizations relying on these email clients for secure communications. The flaw exploits the way Thunderbird handles remote image loading and link processing, creating an unintended data leakage channel that bypasses normal encryption protections.
The technical mechanism of this vulnerability stems from Thunderbird's handling of remote content within decrypted email messages. When an email contains remote images or links, the client may inadvertently expose plaintext email content through the src attribute of these remote elements. This occurs because the email client does not properly sanitize or isolate the decrypted content when rendering remote resources, allowing attackers to craft malicious email content that can leak information through the image loading process. The vulnerability is particularly dangerous because it operates at the rendering layer where decrypted content meets external resource loading, creating a vector for information disclosure that can bypass traditional encryption protections.
The operational impact of this vulnerability extends beyond simple information leakage to potentially enable more sophisticated attacks including targeted data exfiltration and reconnaissance activities. An attacker could craft malicious emails containing remote image references that, when loaded by an affected Thunderbird client, would transmit plaintext email content to attacker-controlled servers. This could result in the exposure of sensitive communications, personal data, or business-critical information that was previously protected by encryption. The vulnerability affects organizations using older Thunderbird versions, making it particularly concerning for enterprises that have not yet upgraded their email client infrastructure.
Organizations should immediately implement security patches and updates to Thunderbird versions 52.8 and later to address this vulnerability. The mitigation strategy should include comprehensive testing of the updated client versions in production environments to ensure compatibility with existing email workflows. Additionally, security teams should consider implementing network-level controls to monitor and restrict access to potentially malicious remote resources, particularly in high-security environments. This vulnerability aligns with CWE-200 (Information Exposure) and could be leveraged as part of broader attack chains in the MITRE ATT&CK framework under the T1071.004 (Application Layer Protocol: DNS) and T1005 (Data from Local System) techniques, emphasizing the need for layered defensive measures including email filtering, network monitoring, and user security awareness training to prevent exploitation of this information disclosure vulnerability.