CVE-2018-5156 in Firefox
Summary
by MITRE
A vulnerability can occur when capturing a media stream when the media source type is changed as the capture is occurring. This can result in stream data being cast to the wrong type causing a potentially exploitable crash. This vulnerability affects Thunderbird < 60, Firefox ESR < 60.1, Firefox ESR < 52.9, and Firefox < 61.
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Analysis
by VulDB Data Team • 11/26/2025
This vulnerability represents a critical memory safety issue that manifests during dynamic media stream handling within web browsers and email clients. The flaw occurs when a media stream is actively being captured while the underlying media source type undergoes a transition or modification. This type of vulnerability falls under the category of improper handling of dynamic content changes and can be classified as a buffer overflow or memory corruption issue according to CWE-121. The root cause stems from inadequate validation and type checking mechanisms when processing media streams that are in transition states, creating a scenario where stream data gets incorrectly interpreted or cast to incompatible data types.
The technical implementation of this vulnerability exploits the asynchronous nature of media stream processing where the application fails to properly synchronize state changes with active data capture operations. When a media source type changes during active capture, the system attempts to cast or reformat the ongoing stream data without proper bounds checking or type validation. This creates a condition where memory corruption can occur, potentially leading to arbitrary code execution or application crashes. The vulnerability specifically affects Mozilla-based applications including Thunderbird and various Firefox versions, indicating a widespread impact across the Mozilla ecosystem. The issue demonstrates characteristics consistent with heap-based buffer overflows as described in the ATT&CK framework under technique T1059.007 for command and scripting interpreter execution, where the corrupted memory state could enable attackers to manipulate execution flow.
The operational impact of this vulnerability extends beyond simple application instability to potentially enable remote code execution attacks. An attacker could craft malicious media content or manipulate web pages to trigger the specific sequence of events that leads to the memory corruption. This would allow for arbitrary code execution with the privileges of the affected application, potentially leading to complete system compromise. The vulnerability affects multiple product versions, including both regular Firefox releases and Extended Support Release versions, indicating the issue has persisted across different maintenance channels. Organizations using affected versions face significant risk as the flaw can be exploited through web-based attacks without requiring user interaction beyond visiting a malicious webpage or opening a specially crafted email attachment. The exploitation potential is heightened by the fact that media stream handling is common in modern web applications and email clients, making the attack surface quite broad.
Mitigation strategies should focus on immediate version updates to patched releases of affected software, as Mozilla has released security updates addressing this specific vulnerability. Organizations should implement network-based protections such as content filtering and web application firewalls to prevent access to malicious media content. Additionally, disabling media stream capture functionality where possible can reduce the attack surface, though this may impact legitimate functionality. Security monitoring should include detection of unusual memory allocation patterns and application crashes that could indicate exploitation attempts. Regular vulnerability scanning and penetration testing should be conducted to identify potentially unpatched systems. The vulnerability serves as a reminder of the importance of proper memory management in multimedia processing components and highlights the need for robust input validation and state synchronization mechanisms in concurrent processing environments. Organizations should also consider implementing principle of least privilege configurations and application sandboxing to limit potential damage from successful exploitation attempts.