CVE-2022-31736 in Thunderbird
Summary
by MITRE • 12/22/2022
A malicious website could have learned the size of a cross-origin resource that supported Range requests. This vulnerability affects Thunderbird < 91.10, Firefox < 101, and Firefox ESR < 91.10.
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Analysis
by VulDB Data Team • 04/15/2025
This vulnerability represents a cross-origin information disclosure issue that exploits the timing characteristics of range request responses to infer the size of cross-origin resources. The flaw exists in the browser's handling of HTTP range requests when accessing resources from different origins, allowing malicious websites to perform side-channel attacks through response size analysis. The vulnerability specifically impacts Firefox browsers and Thunderbird email client, with versions prior to the patched releases being susceptible to this information leakage. The issue stems from the browser's inability to properly mask the response characteristics when serving range requests from cross-origin resources, creating a timing-based channel that reveals sensitive information about the resource size.
The technical implementation of this vulnerability relies on the HTTP range request mechanism, which allows clients to request specific portions of a resource rather than the entire content. When a cross-origin resource supports range requests, the server responds with a Content-Range header indicating the byte range and Content-Length header showing the total size. Malicious actors can exploit this by making multiple range requests with different byte ranges and measuring response times to deduce the total resource size. This timing analysis technique falls under the category of timing side-channel attacks and can be classified as a variant of information leakage through response characteristics. The vulnerability is particularly concerning because it operates at the HTTP protocol level and can be executed through standard web browser functionality without requiring special privileges or user interaction beyond visiting a malicious website.
The operational impact of this vulnerability extends beyond simple information disclosure, as the size of cross-origin resources can reveal sensitive metadata about the underlying content. For example, knowing the size of media files, documents, or other resources can provide insights into file types, content composition, or even potentially sensitive information embedded within the files. This type of information leakage can be particularly damaging in scenarios where the size of resources correlates with confidential data or when combined with other reconnaissance techniques. The vulnerability affects not only web browsers but also email clients like Thunderbird, suggesting that the attack surface extends beyond traditional web browsing contexts. Security researchers have identified this as a potential vector for more sophisticated attacks that could be combined with other vulnerabilities to achieve broader information disclosure objectives.
Mitigation strategies for this vulnerability focus on implementing proper cross-origin resource handling and response timing normalization. Browser vendors have addressed this issue through updates that modify how range requests are processed for cross-origin resources, ensuring that response characteristics do not leak information about the underlying resource size. The recommended approach involves implementing consistent response times for range requests regardless of the actual resource size, and potentially introducing additional checks to prevent timing-based side-channel attacks. Organizations should ensure that all affected browsers and email clients are updated to the latest versions, with particular attention to Firefox ESR releases and Thunderbird installations. Security teams should monitor for any potential exploitation attempts and consider implementing additional network-level controls to detect unusual patterns of range request behavior that might indicate exploitation attempts. This vulnerability aligns with common attack patterns documented in the attack taxonomy, particularly those involving information leakage through timing characteristics and cross-origin resource manipulation, and should be considered as part of broader security monitoring and incident response procedures.