CVE-2026-100822 in Firefox
Summary
by MITRE • 09/29/2026
Spoofing issue in the Networking: HTTP component. This vulnerability was fixed in Firefox ESR 153.4 and Firefox 157.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/29/2026
The identified security flaw resides within the Hypertext Transfer Protocol implementation of Mozilla's networking stack, specifically affecting components responsible for handling HTTP requests and responses. As a spoofing issue, this vulnerability implies that an attacker may be able to manipulate or forge network traffic in a manner that deceives the client application into accepting malicious content as legitimate. In web browsers, such vulnerabilities often stem from improper validation of headers, incorrect handling of redirects, or failures in enforcing strict origin policies during cross-origin requests. The core technical deficiency likely involves a lapse in how the browser distinguishes between trusted and untrusted sources when processing HTTP-based interactions, potentially allowing an adversary to inject spoofed data that appears to originate from a legitimate domain. This type of flaw undermines the fundamental trust model of web communications, where clients rely on server identity verification to ensure data integrity and authenticity.
From an operational perspective, this vulnerability poses significant risks related to session hijacking, credential theft, and man-in-the-middle attacks if exploited in conjunction with other weaknesses such as network sniffing or DNS spoofing. An attacker could potentially intercept HTTP traffic that lacks proper encryption or exploit misconfigurations where mixed content is allowed, thereby injecting malicious scripts or altering page content dynamically. The impact extends beyond simple data interception; it can lead to unauthorized actions performed on behalf of the user if session tokens are compromised through this spoofing mechanism. Furthermore, in enterprise environments relying on Firefox Extended Support Release versions for stability and long-term support, such vulnerabilities require immediate attention as they may remain unpatched longer than those in standard release channels, increasing the window of exposure for organizational assets.
This issue aligns with Common Weakness Enumeration categories related to spoofing attacks, particularly CWE-248 which covers Uncaught Exception scenarios that might lead to unexpected behavior exploitable by attackers, or more specifically CWE-345 Insufficient Verification of Data Authenticity if the flaw involves failing to validate source integrity. In terms of adversary tactics, this vulnerability maps to MITRE ATT&CK techniques involving Network Sniffing and potentially Phishing via Spoofed URLs if the spoofing allows for visual deception in address bars or headers. The exploitation vector typically requires network proximity or prior compromise of a node within the communication path, highlighting the importance of secure transport layer protocols like HTTPS as a primary defense mechanism alongside browser-level mitigations.
To mitigate this risk, organizations should ensure that all affected systems are updated to Firefox ESR 153.4 and Firefox 157 immediately upon availability. Administrators must verify patch deployment across all endpoints using centralized management tools to prevent gaps in coverage. Additionally, enforcing strict Content Security Policies and disabling legacy HTTP features where possible can reduce the attack surface. Users should be educated on recognizing signs of spoofed content, although technical controls remain the primary defense layer. Regular security audits focusing on network traffic handling within browser components are recommended to identify similar latent flaws before they can be leveraged by threat actors for malicious purposes.