CVE-2026-117880 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the XML 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 • 10/28/2026
The identified vulnerability represents a critical memory management error classified as an out-of-bounds write resulting from use-after-free conditions within the Mozilla Firefox XML processing component. This specific flaw arises when the application attempts to access or manipulate memory regions that have already been deallocated by the system's garbage collector or explicit freeing mechanisms. In complex web browsers, the parsing of Extensible Markup Language documents involves intricate object lifecycles where various internal structures are created, referenced, and subsequently destroyed during rendering and layout processes. When a pointer retains reference to an object after its memory has been freed, any subsequent operation on that dangling pointer leads to undefined behavior, typically manifesting as a write to arbitrary memory locations or a crash due to invalid access permissions.
From a technical perspective, this vulnerability falls under the Common Weakness Enumeration category CWE-416, which defines use-after-free errors. The exploitation of such flaws allows attackers to achieve arbitrary code execution with the privileges of the target process. By carefully crafting malicious XML content that triggers the premature deallocation while maintaining active references within the browser's internal state, an attacker can overwrite critical data structures in memory. This capability enables the manipulation of control flow, potentially leading to remote code execution on the victim's system without any user interaction beyond visiting a compromised website or opening a specially crafted file. The severity is heightened by the fact that XML parsing occurs frequently during normal browsing activities involving web pages with embedded structured data or external resources.
The operational impact of this vulnerability extends beyond simple application instability, although denial-of-service conditions are also possible if the memory corruption causes immediate termination of the browser process. More critically, successful exploitation compromises the integrity and confidentiality of user data stored within the browser context, including cookies, session tokens, and potentially saved credentials. This aligns with several techniques in the MITRE ATT&CK framework, particularly T1203 Exploitation for Client Execution and T1059 Command and Scripting Interpreter if subsequent stages involve script execution. The vulnerability affects multiple versions of Firefox, indicating a systemic issue within the XML parsing engine that persisted across significant updates until the specific patches were deployed in Firefox version 159, as well as extended support releases like ESR 115.44 and ESR 153.6.
Mitigation strategies primarily rely on timely software update procedures to apply the vendor-provided fixes which correct the memory management logic within the XML component. Organizations should enforce automated patching policies for all endpoints running affected browser versions to minimize the window of exposure. Additionally, defense-in-depth measures such as enabling strict content security policies and utilizing exploit mitigation technologies like Address Space Layout Randomization can reduce the likelihood of successful exploitation even if a vulnerability is present. Security awareness training remains relevant but secondary in this context since the flaw does not require user interaction beyond standard browsing activities, making technical remediation through version upgrades the most effective countermeasure against potential remote code execution attacks targeting these specific Firefox releases.