CVE-2017-7787 in Firefox
Summary
by MITRE
Same-origin policy protections can be bypassed on pages with embedded iframes during page reloads, allowing the iframes to access content on the top level page, leading to information disclosure. This vulnerability affects Thunderbird < 52.3, Firefox ESR < 52.3, and Firefox < 55.
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Analysis
by VulDB Data Team • 01/09/2021
The vulnerability described in CVE-2017-7787 represents a critical breach of web browser security mechanisms that undermines fundamental isolation principles governing web content execution. This flaw specifically targets the same-origin policy implementation within Mozilla-based browsers including Thunderbird, Firefox ESR, and Firefox versions prior to their respective secure releases. The vulnerability manifests during page reload operations when embedded iframe elements maintain access to parent page content, creating an unexpected information disclosure scenario that violates core web security assumptions.
The technical mechanism behind this vulnerability involves a race condition or timing issue during page reload processes where the browser's security context management fails to properly enforce cross-origin restrictions. When a page containing embedded iframes is reloaded, the security boundaries that normally prevent iframe content from accessing parent page data become temporarily compromised. This occurs because the browser's internal state management does not adequately synchronize the security contexts between the top-level page and its embedded content during the reload transition period. The flaw essentially allows malicious or compromised iframe content to execute code that can access sensitive information from the parent page, including cookies, local storage, and other potentially confidential data.
From an operational impact perspective, this vulnerability creates significant risk for users of affected browser versions as it enables sophisticated attacks that could exfiltrate sensitive user data without user awareness. Attackers could leverage this weakness to construct malicious websites that embed iframes pointing to compromised third-party services, then trigger page reloads to gain access to user sessions, personal information, or other confidential data stored in the parent browsing context. The vulnerability is particularly dangerous because it operates silently during normal user browsing activities, making detection extremely difficult for both users and security monitoring systems. This type of information disclosure could lead to identity theft, session hijacking, and unauthorized access to personal accounts or corporate data.
Security mitigations for CVE-2017-7787 primarily involve updating to patched versions of the affected software, specifically Firefox 55, Firefox ESR 52.3, and Thunderbird 52.3, which contain fixes that properly enforce same-origin policy boundaries during page reload operations. Organizations should prioritize immediate deployment of these security updates across all affected systems, particularly in enterprise environments where user exposure to malicious content is higher. Additionally, administrators can implement browser security policies that limit iframe usage and enforce stricter content security policies, though these measures serve as supplementary protections rather than complete solutions. The vulnerability aligns with CWE-200, which addresses improper output neutralization for logs, and relates to ATT&CK technique T1071.004 for application layer protocol, though the specific attack vector involves browser security boundary violations rather than network protocol manipulation. Regular security assessments should include verification that affected browsers have been properly updated and that no legacy versions remain in use within the organization's infrastructure.