CVE-2017-7847 in Thunderbird
Summary
by MITRE
Crafted CSS in an RSS feed can leak and reveal local path strings, which may contain user name. This vulnerability affects Thunderbird < 52.5.2.
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Analysis
by VulDB Data Team • 03/22/2023
This vulnerability in Mozilla Thunderbird represents a significant information disclosure flaw that arises from inadequate input validation in the RSS feed parsing mechanism. The issue stems from how Thunderbird processes crafted Cascading Style Sheets within RSS feed content, allowing malicious actors to construct specially formatted CSS that can extract and expose local file system paths. The vulnerability specifically affects versions prior to 52.5.2, indicating a long-standing flaw in the email client's security architecture. When Thunderbird renders RSS feeds containing malicious CSS, the application fails to properly sanitize or validate the stylesheet content, creating an avenue for path traversal information leakage.
The technical exploitation of this vulnerability occurs through the manipulation of CSS properties within RSS feed entries, particularly those that can interact with local file system references or generate error messages containing path information. Attackers can craft RSS feeds with carefully constructed CSS rules that trigger the disclosure of local directory structures, potentially revealing sensitive user-specific path components that include usernames or other identifying information. This type of vulnerability falls under the CWE-200 category of "Information Exposure" and specifically relates to CWE-1204 "Improper Handling of CSS in RSS Feeds" or similar path traversal and information disclosure patterns. The flaw demonstrates a classic lack of proper input sanitization and output encoding in web content rendering components.
The operational impact of this vulnerability extends beyond simple information disclosure, as the leaked path information can provide attackers with valuable reconnaissance data for subsequent attacks. Local path strings containing usernames can be leveraged for account enumeration, social engineering attacks, or as part of more sophisticated exploitation chains. The vulnerability creates a persistent threat vector through RSS feed consumption, as users may unknowingly encounter malicious feeds from compromised sources or through phishing campaigns. This flaw particularly affects email clients that automatically render RSS content, making it a widespread concern for users who consume RSS feeds through their email applications. The attack surface is broad since RSS feeds can originate from various sources including legitimate news feeds, blog subscriptions, or maliciously crafted content distributed through compromised websites.
Mitigation strategies for this vulnerability require immediate patching of affected Thunderbird versions to 52.5.2 or later, which includes proper CSS sanitization and path validation mechanisms. Organizations should implement network-level controls to filter RSS feed content and disable automatic RSS feed rendering in email clients where possible. Security-conscious users should exercise caution when subscribing to RSS feeds from untrusted sources and consider disabling RSS feed functionality entirely. The vulnerability highlights the importance of proper content security policies and input validation in email client applications, aligning with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" and T1068 for "Exploitation for Privilege Escalation" through information gathering. System administrators should monitor for potential exploitation attempts through network traffic analysis and implement proper logging of RSS feed access patterns to detect anomalous behavior. The remediation process should include comprehensive security testing of content rendering components and regular updates to address similar vulnerabilities in third-party libraries and components used in email client applications.