CVE-2026-100828 in Firefox
Summary
by MITRE • 09/29/2026
Mitigation bypass in the Bookmarks & History component. This vulnerability was fixed in Firefox ESR 153.4 and Firefox 157.
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Analysis
by VulDB Data Team • 09/29/2026
The identified security issue resides within the bookmarks and history management subsystem of Mozilla Firefox, specifically affecting versions prior to ESR 153.4 and version 157. This vulnerability is characterized by a mitigation bypass, indicating that existing defensive mechanisms designed to restrict or monitor user interactions with browsing data were circumvented through specific exploitation techniques. In modern web browsers, the bookmarks and history components serve as critical interfaces for managing persistent state information about visited URLs and saved links. These subsystems are frequently targeted because they hold sensitive contextual data regarding a user's digital footprint and preferences. The presence of a mitigation bypass suggests that security controls such as content policy restrictions, permission checks, or sandboxing boundaries intended to limit how scripts or extensions interact with this data were not properly enforced under certain conditions.
From a technical perspective, vulnerabilities in the bookmarks and history components often stem from improper validation of input parameters passed during API calls or DOM manipulation events. Attackers may leverage cross-site scripting vectors, privilege escalation via malicious add-ons, or race conditions within the asynchronous handling of bookmark updates to bypass these mitigations. The flaw likely allows an attacker with limited initial access privileges to perform actions that should be restricted by default security policies. For instance, this could involve unauthorized reading of history data from other tabs or contexts where such access is prohibited, or potentially modifying bookmarks in a way that facilitates phishing attacks or redirects users to malicious domains without proper user consent indicators. The bypass mechanism implies that the browser's internal logic failed to correctly evaluate the context of the request against its security policy database before executing the operation.
The operational impact of this vulnerability extends beyond simple data leakage, as it undermines the integrity of the browsing experience and trust in the browser's security model. Users relying on Firefox for secure web navigation may find their privacy compromised if sensitive history entries are exposed to malicious scripts or extensions that should not have access to such information. Furthermore, the ability to manipulate bookmarks without proper authorization can lead to social engineering attacks where attackers insert deceptive links into a user’s bookmark bar, increasing the likelihood of credential theft or malware distribution when those links are clicked later. This type of vulnerability erodes confidence in the browser's ability to isolate untrusted content from sensitive local data stores, which is a fundamental principle of modern web security architectures.
Industry standards classify such issues under categories related to improper access control and privilege escalation within client-side applications. The Common Weakness Enumeration (CWE) database likely maps this vulnerability to CWE-269 Improper Privilege Management or CWE-749 Exposed Dangerous Method, depending on the specific mechanism of the bypass. In terms of offensive security frameworks like MITRE ATT&CK for Enterprise and Mobile, this behavior aligns with techniques involving collection of browser history data or modification of application settings to facilitate further attacks. The vulnerability highlights the complexity involved in maintaining strict boundaries between different execution contexts within a single-process or multi-process architecture, especially when dealing with persistent storage mechanisms that require frequent read-write operations.
To mitigate the risks associated with this flaw, users must upgrade their Firefox installation immediately to version 157 for standard releases or ESR 153.4 for extended support release channels. These updates contain patches that reinforce the validation logic within the bookmarks and history subsystems, ensuring that all access requests are properly authenticated and authorized according to current security policies. Administrators managing enterprise deployments should verify that endpoint protection systems flag any attempts to exploit this specific component before patching is applied across the network. Additionally, users can reduce their exposure by disabling unnecessary extensions that request broad permissions related to browsing history or bookmarks, as these add-ons are often the vector through which such mitigations are bypassed in real-world scenarios. Regularly updating browser software remains the most effective defense against emerging vulnerabilities of this nature.