CVE-2026-117973 in Firefox
Summary
by MITRE • 10/27/2026
Use-after-free in the Networking: DNS component. This vulnerability was fixed in Firefox 159 and Firefox ESR 153.6.
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Analysis
by VulDB Data Team • 10/27/2026
The identified vulnerability represents a critical memory management error within the Domain Name System (DNS) resolution subsystem of Mozilla Firefox, specifically classified as an out-of-bounds write resulting from use-after-free conditions. This type of flaw occurs when the application attempts to access or modify memory that has already been deallocated by the system's garbage collector or explicit free operations. In the context of networked applications like web browsers, DNS resolution is a high-frequency operation where objects representing pending queries are created and destroyed rapidly. If the internal state management fails to properly nullify pointers after freeing these structures, subsequent asynchronous callbacks or event handlers may inadvertently reference stale memory addresses. This creates a window of opportunity for an attacker who can influence the timing of network requests or manipulate DNS responses to trigger this race condition. The technical severity stems from the fact that use-after-free vulnerabilities allow for arbitrary read and write operations in the process's address space, which is often considered one of the most dangerous classes of software defects due to its potential for complete system compromise.
From an operational perspective, exploitation of this vulnerability could lead to remote code execution on a victim's machine without any user interaction beyond visiting a maliciously crafted webpage or being subjected to a DNS-based attack vector such as cache poisoning or response spoofing. An attacker could craft specific DNS responses that cause the browser to free certain internal structures while leaving pointers active, then trigger operations that reallocate those freed memory regions with controlled data. By carefully controlling this allocation, the attacker can overwrite function pointers or object vtables within the Firefox process space. This mechanism enables the execution of arbitrary shellcode in the context of the user's privileges, potentially leading to full system takeover if the browser is running with elevated permissions or if additional vulnerabilities are chained together. The impact extends beyond individual device compromise as it undermines the integrity and confidentiality of web browsing sessions, allowing for session hijacking, credential theft, and installation of persistent malware backdoors through drive-by download techniques facilitated by the initial code execution.
Industry standards categorize this flaw under CWE-416, which denotes Use After Free vulnerabilities, highlighting the failure to manage object lifecycles correctly within dynamic memory environments. Furthermore, in terms of tactical behavior, exploitation aligns with MITRE ATT&CK technique T1203, specifically referencing Exploitation for Client Execution, where attackers leverage software flaws to execute malicious code on target systems via client-side applications like browsers. The vulnerability was addressed in Firefox version 159 and the Extended Support Release (ESR) version 153.6 through rigorous memory safety improvements likely involving Rust-based rewrites or enhanced pointer validation checks within the networking stack. These updates ensure that references to DNS-related objects are invalidated immediately upon deallocation, preventing any subsequent access attempts from succeeding against freed memory regions.
To mitigate risks associated with this class of vulnerabilities, organizations and individual users must prioritize timely patch management strategies ensuring all instances of Firefox are updated to version 159 or later for standard releases and 153.6 or later for enterprise environments. Security teams should also implement network-level defenses such as DNSSEC validation to prevent response spoofing attacks that might attempt to trigger the race condition, although this does not replace the need for software patching since client-side memory corruption can often be triggered by local redirects or compromised CDNs. Additionally, deploying browser isolation technologies or sandboxing solutions can limit the blast radius of any successful exploitation event by restricting the privileges and system access available to the browser process in the event that a vulnerability is bypassed. Continuous monitoring for anomalous network behavior related to DNS queries may also provide early detection indicators of attempted exploitation activities targeting this specific flaw before it leads to full compromise.