CVE-2026-117956 in Firefox
Summary
by MITRE • 10/27/2026
Invalid pointer in the Nimbus Desktop Client 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 security issue resides within the Nimbus Desktop Client, a core component of Mozilla's telemetry and experimentation infrastructure used to manage feature flags and remote configuration for Firefox browsers. The specific flaw involves an invalid pointer dereference, which typically occurs when software attempts to access memory that has not been properly allocated or has already been freed. In the context of C++ based applications like Firefox, such errors often stem from race conditions during object lifecycle management, where a reference is retained after the underlying object has been destroyed, or from insufficient validation of pointer values before use. This type of vulnerability falls squarely under CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer and more specifically CWE-416 Use After Free if the memory was previously deallocated, or CWE-825 Expired Pointer Dereference if the pointer points to an invalid address range.
From an operational perspective, this vulnerability poses significant risks depending on how it is triggered. If exploited successfully through a crafted configuration payload delivered via the Nimbus service, it could lead to application crashes resulting in denial of service conditions for end users. More critically, improper memory handling can sometimes be leveraged to achieve arbitrary code execution if an attacker can control the data written into or read from the invalid pointer location. This aligns with ATT&CK technique T1203 Exploitation for Client Execution, where attackers exploit software vulnerabilities in client-side applications to gain initial access or persistence on a victim's system. Although Nimbus primarily handles configuration data rather than user-facing content rendering engines like Gecko, the complexity of modern browser architectures means that memory corruption bugs can potentially impact broader security boundaries if they lead to state corruption within shared processes.
The resolution for this vulnerability was implemented in Firefox version 159 and Firefox Extended Support Release (ESR) version 153.6. These updates include code changes designed to validate pointer states before access, ensure proper synchronization of object lifecycles, or implement safer memory management practices such as using smart pointers instead of raw pointers where applicable. Organizations relying on these browser versions should verify that their deployment pipelines have applied the latest patches to mitigate this risk. For users who cannot immediately update, monitoring for unusual behavior in the Nimbus client process and ensuring strict network policies can limit exposure to malicious configuration sources remains a prudent defensive measure until full patching is achieved across all endpoints.