CVE-2017-7835 in Firefox
Summary
by MITRE
Mixed content blocking of insecure (HTTP) sub-resources in a secure (HTTPS) document was not correctly applied for resources that redirect from HTTPS to HTTP, allowing content that should be blocked, such as scripts, to be loaded on a page. This vulnerability affects Firefox < 57.
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Analysis
by VulDB Data Team • 03/22/2023
The vulnerability described in CVE-2017-7835 represents a critical flaw in Firefox's mixed content blocking mechanism that undermines the security of HTTPS-protected web pages. This issue specifically targets the browser's ability to prevent loading of insecure HTTP resources within secure HTTPS contexts, creating a potential attack vector for man-in-the-middle scenarios and credential theft. The vulnerability affects Firefox versions prior to 57, where the security implementation failed to properly handle redirect chains that begin with HTTPS and transition to HTTP, thereby allowing malicious actors to bypass intended security protections.
The technical flaw stems from Firefox's insufficient validation of resource loading sequences when dealing with HTTP redirects from HTTPS origins. When a web page loads over HTTPS and attempts to fetch sub-resources that redirect from HTTPS to HTTP, the browser's mixed content blocking logic fails to recognize that these redirected resources should be blocked. This occurs because the security check is performed at the initial HTTPS request level rather than following the complete redirect chain, allowing HTTP resources to be loaded despite the secure context. This behavior violates fundamental security principles of content security and creates a scenario where attackers can inject malicious scripts or steal sensitive data through seemingly secure pages.
The operational impact of this vulnerability is significant as it enables attackers to exploit the trust relationship between users and secure websites. When users visit HTTPS sites, they expect all content to be delivered securely, but this flaw allows attackers to inject insecure resources that can execute malicious code, steal session cookies, or perform other harmful actions. The vulnerability particularly affects web applications that rely on mixed content blocking to prevent attacks such as cross-site scripting or credential harvesting, making it a serious concern for financial institutions, social media platforms, and any service handling sensitive user data. This issue directly relates to CWE-346, which addresses "Improper Verification of Source of a Communication Channel", and aligns with ATT&CK technique T1071.004 for application layer protocol manipulation.
Mitigation strategies for this vulnerability require immediate browser updates to Firefox version 57 or later, where the mixed content blocking mechanism has been properly implemented to follow redirect chains. System administrators should ensure all users are running patched versions of Firefox and consider implementing additional security measures such as content security policies to further protect against mixed content attacks. Organizations should also monitor their web applications for insecure resource references and implement proper redirect handling to prevent similar issues in custom implementations. The fix implemented in Firefox 57 demonstrates the importance of comprehensive security testing that includes redirect chain validation and proper handling of HTTP-to-HTTPS transitions. This vulnerability serves as a reminder of the critical importance of proper mixed content handling in web browsers and the potential consequences when security mechanisms fail to account for complex request flows.