CVE-2026-74983 in Firefox
Summary
by MITRE • 08/18/2026
Mitigation bypass in the Data Loss Prevention component. This vulnerability was fixed in Firefox 154, Firefox ESR 140.14, and Firefox ESR 153.1.
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Analysis
by VulDB Data Team • 08/18/2026
The identified vulnerability represents a critical failure within Mozilla Firefox's Data Loss Prevention (DLP) subsystem, specifically involving the bypass of security controls designed to restrict or monitor sensitive data exfiltration. In enterprise environments where browsers are deployed as part of broader endpoint protection strategies, DLP components serve as essential gatekeepers that prevent users from inadvertently or maliciously transmitting confidential information such as intellectual property, personally identifiable information, or financial records outside authorized channels. The flaw allows an attacker to circumvent these protective mechanisms, effectively rendering the DLP policies ineffective against specific attack vectors. This bypass capability undermines the integrity of organizational security postures that rely on browser-based enforcement for data governance and compliance with regulations such as GDPR, HIPAA, or PCI-DSS.
From a technical perspective, this vulnerability likely stems from an improper validation logic or state management error within the DLP engine's interaction with web content or extension APIs. Such flaws often arise when the security module fails to consistently apply restrictions across all execution contexts, including iframes, service workers, or dynamically loaded scripts. An adversary could exploit this by crafting a malicious webpage that triggers specific browser behaviors which are not adequately inspected by the DLP filter. For instance, an attacker might utilize obfuscated JavaScript techniques or manipulate HTTP headers and request methods to send data through channels that were incorrectly classified as safe or unmonitored by the vulnerability's logic. The absence of rigorous boundary checks allows sensitive payloads to escape detection, leading to unauthorized data transmission without triggering alerts or blocking actions defined in the local security policy.
The operational impact of this flaw is significant for organizations utilizing Firefox with strict DLP configurations. It enables potential insider threats or external attackers who have gained access to a user's session to exfiltrate high-value assets undetected. This can result in severe financial losses, reputational damage, and legal liabilities due to non-compliance with data protection laws. Furthermore, the existence of such a bypass erodes trust in automated security controls, forcing administrators to rely on more labor-intensive manual monitoring or less efficient workarounds that may introduce new vulnerabilities. The risk is compounded if the browser is used for accessing sensitive corporate applications where session cookies or form data are routinely transmitted; an attacker could harvest these credentials and exfiltrate them before any DLP alert is generated, facilitating further lateral movement within the network.
To address this issue, immediate remediation requires updating all affected Firefox installations to version 154, Firefox ESR 140.14, or Firefox ESR 153.1, as these releases contain the necessary patches that correct the validation logic and close the bypass pathways. Organizations should verify patch deployment across their entire fleet using centralized management tools to ensure no endpoints remain vulnerable during the transition period. In addition to software updates, security teams should review existing DLP policies to identify any edge cases where manual overrides or exceptions might have been configured incorrectly, potentially exacerbating the risk of exploitation. Implementing network-level monitoring and anomaly detection can provide a secondary layer of defense, alerting administrators to unusual data transfer patterns that may indicate an active attempt to exploit this vulnerability before it is fully patched on all devices.
This incident aligns with common weakness classifications such as CWE-20 Improper Input Validation or CWE-798 Use of Hard-coded Credentials if the bypass involves authentication tokens, and falls under MITRE ATT&CK techniques related to Exfiltration Over C2 Channels or Command and Control protocols where attackers use legitimate applications for data theft. By treating this vulnerability with high priority and ensuring comprehensive patch management, organizations can restore the effectiveness of their browser-based DLP controls and maintain compliance with stringent security standards. Continuous monitoring and regular penetration testing should be employed to validate that the patched implementation correctly enforces restrictions across all supported web technologies and API interactions within the Firefox environment.