CVE-2026-117992 in Firefox
Summary
by MITRE • 10/27/2026
Information disclosure in the CSS Parsing and Computation component. This vulnerability was fixed in Firefox 159, Firefox ESR 115.44, and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability resides within the Cascading Style Sheets parsing and computation engine of Mozilla Firefox, representing a critical class of information disclosure flaws that can inadvertently expose internal browser state or sensitive data to malicious web content. This component is responsible for interpreting CSS rules applied to HTML documents, calculating computed styles based on inheritance and specificity, and managing how visual properties are resolved across different elements. When this subsystem contains logic errors during the parsing phase or when computing final style values, it may allow an attacker to read memory contents that were not intended to be accessible via standard web APIs. Such vulnerabilities typically arise from improper bounds checking, race conditions in asynchronous rendering pipelines, or mishandling of specific CSS properties that trigger undefined behavior within the underlying C++ codebase. The exploitation of this flaw does not require user interaction beyond visiting a maliciously crafted webpage, making it particularly dangerous for users who browse untrusted sites or are targeted by drive-by download attacks.
From a technical perspective, information disclosure vulnerabilities in browser rendering engines often stem from how style data is stored and retrieved during the layout process. If the CSS engine fails to properly isolate computed styles between different browsing contexts or if it leaks pointers to internal structures into JavaScript-accessible objects, an attacker can construct scripts that read these values byte by byte. This capability effectively bypasses same-origin policies in specific edge cases where style computation intersects with memory management routines. The flaw likely involves a scenario where the browser exposes sensitive information such as stack addresses, heap layouts, or potentially data from other tabs if sandboxing mechanisms are circumvented through this side channel. By analyzing timing differences or direct value retrieval, an attacker can reconstruct critical security boundaries that protect user privacy and application integrity.
The operational impact of this vulnerability is severe because it undermines the fundamental trust model of web browsers. Browsers rely on strict isolation between different sources to prevent cross-site scripting attacks from escalating into full system compromise. When information disclosure occurs at the CSS parsing level, it provides attackers with valuable reconnaissance data that can facilitate further exploitation steps. For instance, knowing memory layout details allows for more reliable exploitation of other vulnerabilities such as buffer overflows or use-after-free conditions by defeating address space layout randomization techniques. Furthermore, if sensitive user data is inadvertently exposed through style properties, it could lead to privacy breaches where personal information stored in web applications becomes visible to third-party scripts embedded on the page. This erodes confidence in the browser's ability to protect user sessions and confidential communications.
Mitigation strategies primarily involve applying the vendor-provided updates that address these specific code paths within the CSS engine. Users must ensure they are running Firefox version 159 or later, as well as the extended support release versions 115.44 and 153.6, which contain patches for this issue. These updates likely include fixes to input validation routines, improved memory safety checks during style computation, and stricter enforcement of isolation boundaries between different document contexts. In addition to updating software, organizations should implement content security policies that restrict the execution of inline scripts and limit access to certain browser APIs where possible. Regular monitoring of vulnerability databases for new disclosures related to rendering engines is also recommended to maintain a robust defense posture against evolving threats targeting web browsers.
This incident aligns with common weakness enumeration categories such as CWE-200, which covers exposure of sensitive information to unauthorized actors, and potentially CWE-125 if it involves out-of-bounds read operations leading to memory leakage. In the context of the MITRE ATT&CK framework, this vulnerability supports reconnaissance tactics by providing attackers with environmental data that aids in crafting more precise exploits against targeted systems. The fix emphasizes the importance of rigorous code review processes for complex subsystems like style computation engines, where subtle logic errors can have significant security implications due to their pervasive use across all web pages viewed by users.