CVE-2019-25136 in Firefox
Summary
by MITRE • 06/19/2023
A compromised child process could have injected XBL Bindings into privileged CSS rules, resulting in arbitrary code execution and a sandbox escape. This vulnerability affects Firefox < 70.
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Analysis
by VulDB Data Team • 12/11/2024
This vulnerability represents a critical sandbox escape flaw in Mozilla Firefox that stems from improper handling of XBL (XML Binding Language) bindings within privileged CSS contexts. The issue arises when a compromised child process manages to inject malicious XBL bindings into privileged CSS rules, creating a pathway for arbitrary code execution that bypasses Firefox's security boundaries. The vulnerability specifically affects Firefox versions prior to 70, indicating a long-standing flaw in the browser's security architecture that allowed untrusted content to manipulate privileged execution contexts.
The technical exploitation of this vulnerability involves a sophisticated attack vector where malicious code running in a compromised child process can inject XBL bindings that are then processed within privileged CSS rules. XBL bindings are typically used to extend HTML elements with custom behavior and are normally restricted to privileged contexts to prevent security breaches. However, this flaw allows unprivileged code to manipulate these bindings in ways that should be impossible, effectively creating a bridge between untrusted and trusted execution environments. The flaw operates at the intersection of Firefox's CSS engine and XBL processing subsystems, where the boundary checking mechanism fails to properly validate the source and integrity of XBL bindings being applied to privileged CSS rules.
The operational impact of this vulnerability is severe and far-reaching, as it enables attackers to completely bypass Firefox's sandboxing mechanisms that are designed to isolate untrusted content from the browser's core processes. Once exploited, the vulnerability allows an attacker to execute arbitrary code with the privileges of the browser process itself, potentially leading to full system compromise. This type of sandbox escape is particularly dangerous because it undermines the fundamental security model that browsers use to protect users from malicious websites and downloads. The vulnerability essentially allows attackers to break out of the restricted environment where web content runs and gain access to system resources that should remain protected.
Mitigation strategies for this vulnerability include immediate upgrade to Firefox version 70 or later, which contains the necessary patches to address the XBL binding injection flaw. Organizations should also implement additional security measures such as content security policies, strict sandboxing configurations, and regular security assessments to prevent exploitation. The vulnerability aligns with CWE-276, which addresses improper privilege management, and maps to ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation typically involves executing malicious code within the browser's privileged context. Security teams should also monitor for indicators of compromise related to unusual XBL binding behavior and implement network-level controls to prevent access to known malicious domains that might attempt to exploit this vulnerability.