CVE-2026-109779 in Firefox
Summary
by MITRE • 10/13/2026
Race condition in the Networking: DNS component. This vulnerability was fixed in Firefox 158.
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Analysis
by VulDB Data Team • 10/13/2026
The identified security flaw resides within the Domain Name System resolution subsystem of Mozilla Firefox, specifically affecting the networking layer responsible for translating domain names into IP addresses. A race condition implies a situation where the system's behavior depends on the relative timing or interleaving of multiple uncontrollable events, such as concurrent threads accessing shared data without proper synchronization mechanisms. In this specific context, the vulnerability likely involves improper handling of state changes during DNS queries, potentially allowing an attacker to manipulate the resolution process by exploiting the window between a request being initiated and its completion. This type of flaw is particularly dangerous because it can lead to unpredictable behavior that may bypass standard security checks or result in the browser resolving malicious domains instead of legitimate ones.
From a technical perspective, race conditions in DNS handling often stem from insufficient locking mechanisms when updating internal caches or response handlers. If an attacker can trigger multiple concurrent requests for the same domain or manipulate network responses during this critical window, they may force the application to accept spoofed data before it has been fully validated. This could result in a scenario where malicious content is loaded under the guise of a trusted site, effectively facilitating phishing attacks or cross-site scripting if combined with other vulnerabilities. The complexity of modern networking stacks increases the likelihood of such timing errors, especially when asynchronous operations are involved and shared resources like DNS caches are accessed by multiple threads simultaneously without adequate mutual exclusion primitives.
The operational impact of this vulnerability is significant for end-users relying on Firefox for secure web browsing. Successful exploitation could allow an attacker to redirect traffic to malicious servers, leading to credential theft, malware distribution, or session hijacking. Since DNS resolution is a fundamental step in almost every internet interaction, compromising its integrity undermines the trust model that browsers use to ensure users are connecting to legitimate entities. Users might inadvertently interact with phishing sites that mimic legitimate services because their browser was tricked into resolving those domains incorrectly. This erosion of trust can have severe consequences for personal privacy and financial security, particularly if sensitive information is entered on compromised pages.
To mitigate the risks associated with this vulnerability, users are strongly advised to update Mozilla Firefox immediately to version 158 or later, where these timing issues have been addressed through improved synchronization logic within the DNS component. Organizations should enforce automated patch management policies to ensure that all endpoints running affected versions of the browser are updated promptly. Additionally, implementing network-level monitoring can help detect anomalous DNS traffic patterns that might indicate exploitation attempts. Security teams should also review their incident response plans to include scenarios involving compromised DNS resolution and educate users on recognizing signs of potential phishing or man-in-the-middle attacks.
This vulnerability aligns with Common Weakness Enumeration category CWE-362, which covers concurrent execution race conditions leading to state corruption. It also relates to MITRE ATT&CK techniques such as T1071 Application Layer Protocol for command and control communications via DNS tunneling or redirection. By addressing the underlying synchronization flaws in the networking stack, Mozilla has reinforced the browser's resilience against timing-based attacks that seek to subvert secure communication channels. Continuous monitoring of vendor security advisories remains essential for maintaining a robust defense posture against evolving threats targeting core web technologies.