CVE-2026-100771 in Firefox
Summary
by MITRE • 09/29/2026
Undefined behavior in the DOM: Streams component. This vulnerability was fixed in Firefox ESR 153.4, Firefox 157, Firefox ESR 115.42, and Firefox ESR 140.17.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 09/29/2026
The identified vulnerability resides within the Document Object Model Streams component of Mozilla Firefox browsers, representing a critical instance of undefined behavior that can lead to severe security implications. This flaw was addressed in recent updates including Firefox ESR version 153.4, standard release versions such as Firefox 157, and extended support releases like Firefox ESR 115.42 and Firefox ESR 140.17. The core issue stems from improper handling of stream operations within the DOM API, where specific edge cases or malformed inputs can trigger states that are not explicitly defined by the ECMAScript specification or browser implementation guidelines. Such undefined behavior often manifests as memory corruption, data inconsistency, or unexpected execution flows, which attackers can potentially exploit to achieve arbitrary code execution or cause denial of service conditions against affected systems.
From a technical perspective, this vulnerability aligns with CWE-758, Reliance on Undefined, Unspecified, or Implementation-Dependent Behavior, and may also intersect with CWE-120, Buffer Overflow without description of buffer size, if the undefined behavior involves memory management errors within the stream processing logic. The DOM Streams API is designed to provide a high-level abstraction for reading and writing data streams, but when internal state transitions are not rigorously validated or when race conditions occur during asynchronous operations, the browser may enter an unstable state. This instability can be leveraged by malicious web content that carefully crafts specific sequence of stream reads, writes, or cancellations to trigger the flaw. The impact is particularly significant because it affects the core rendering and networking layers of the browser, potentially allowing a remote attacker who convinces a user to visit a compromised website to execute code with the privileges of the victim's process.
The operational impact of this vulnerability extends beyond simple application crashes or data leakage. If exploited successfully, an attacker could bypass security controls such as the Same-Origin Policy by manipulating internal state variables that govern access permissions for stream resources. This could lead to information disclosure where sensitive data from other tabs or applications is exposed through side-channel effects resulting from memory corruption. Furthermore, in enterprise environments relying on Extended Support Releases like ESR 153.4 and ESR 140.17, the presence of this vulnerability poses a persistent risk until patches are deployed across all endpoints. The availability of fixes in multiple branches indicates that the issue was present for some time or affected different code paths depending on the browser version, necessitating comprehensive patch management strategies to ensure complete mitigation.
Mitigation requires immediate deployment of the specified Firefox updates by system administrators and end-users alike. Organizations should prioritize updating their ESR installations given their longer lifecycle and typical use in corporate environments where stability is paramount but security patches are sometimes delayed. Additionally, implementing browser hardening techniques such as disabling unnecessary JavaScript features or using content security policies can reduce the attack surface available to exploit this vulnerability. Security teams should also monitor for indicators of compromise related to unusual memory usage patterns or unexpected network activity originating from browser processes, which may signal an active exploitation attempt targeting this undefined behavior flaw in the DOM Streams component.