CVE-2018-5091 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur during WebRTC connections when interacting with the DTMF timers. This results in a potentially exploitable crash. This vulnerability affects Firefox ESR < 52.6 and Firefox < 58.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5091 represents a critical use-after-free condition within the WebRTC implementation of Mozilla Firefox browsers. This flaw specifically manifests during the handling of DTMF (Dual-Tone Multi-Frequency) timer interactions within WebRTC connections, creating a scenario where memory previously deallocated is accessed by the application, potentially leading to arbitrary code execution. The vulnerability stems from inadequate memory management practices during the processing of telephony signaling data within the browser's WebRTC stack, where the DTMF timer mechanism fails to properly validate object references after memory deallocation.
The technical exploitation of this vulnerability occurs when a malicious web page triggers a WebRTC connection with specific DTMF timer parameters that cause the browser to access freed memory locations. This use-after-free condition falls under the Common Weakness Enumeration category CWE-416, which specifically addresses the use of freed memory, and represents a fundamental flaw in the application's memory management. The vulnerability is particularly concerning because WebRTC functionality is widely used for real-time communication in web applications, making the attack surface expansive across various legitimate use cases including video conferencing, voice calls, and real-time collaboration platforms.
Operationally, this vulnerability poses significant risks to Firefox users running affected versions, as it can be exploited through malicious websites without requiring user interaction beyond visiting the compromised page. The crash condition that results from this vulnerability can be leveraged by attackers to execute arbitrary code with the privileges of the browser process, potentially leading to complete system compromise. The impact extends beyond individual user devices as the vulnerability affects both Firefox ESR 52.x releases and Firefox 58.x versions, representing a substantial portion of the browser's user base at the time of discovery. This vulnerability aligns with ATT&CK technique T1059.007 for command and script interpreter execution, as successful exploitation could enable attackers to establish persistent access through malicious code execution.
The security implications of CVE-2018-5091 are exacerbated by the fact that WebRTC connections are commonly established through standard web page interactions, making exploitation relatively straightforward for threat actors. The vulnerability demonstrates poor input validation and memory management practices within Firefox's WebRTC implementation, specifically in how DTMF timer objects are handled during connection lifecycle events. Organizations and users must immediately upgrade to Firefox versions 52.6 ESR or 58.0 and later to mitigate this risk, as the vulnerability cannot be effectively patched through configuration changes or workarounds. The flaw represents a critical security gap that requires immediate remediation to prevent potential exploitation in the wild, particularly given the widespread adoption of Firefox and the prevalence of WebRTC-based applications in modern web environments.