CVE-2017-7819 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur in design mode when image objects are resized if objects referenced during the resizing have been freed from memory. This results in a potentially exploitable crash. This vulnerability affects Firefox < 56, Firefox ESR < 52.4, and Thunderbird < 52.4.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2017-7819 represents a critical use-after-free condition that manifests within the Firefox browser's image handling functionality during design mode operations. This flaw specifically occurs when users resize image objects while the browser is in design mode, creating a scenario where memory management becomes compromised due to improper object lifecycle handling. The issue stems from the browser's failure to properly track object references during dynamic resizing operations, leading to situations where previously freed memory locations are accessed after deallocation. This particular vulnerability demonstrates a classic memory safety issue that has long been a target for exploitation by malicious actors seeking to compromise browser security.
The technical implementation of this vulnerability resides in the browser's rendering engine where image objects undergo dynamic modification during user interaction. When users manipulate image dimensions in design mode, the underlying code attempts to reference objects that may have already been removed from memory through garbage collection or explicit deallocation processes. This creates a scenario where the application attempts to access memory that has been freed, potentially allowing attackers to control the execution flow through carefully crafted input sequences. The vulnerability is particularly concerning because it occurs during normal user operations rather than in specialized attack scenarios, making it more accessible to threat actors. According to CWE classification, this corresponds to CWE-416 Use After Free, which is categorized as a memory safety issue that directly enables arbitrary code execution capabilities. The ATT&CK framework would classify this vulnerability under T1059 Command and Scripting Interpreter and potentially T1203 Exploitation for Client Execution, as it provides a pathway for remote code execution through browser-based attacks.
The operational impact of this vulnerability extends beyond simple browser instability, as it creates a potential vector for sophisticated attacks targeting end users. When exploited, the crash condition can be manipulated to execute arbitrary code with the privileges of the browser process, potentially leading to complete system compromise. The affected software versions represent a significant portion of the browser user base at the time of discovery, making this vulnerability particularly dangerous as it could affect millions of users. Organizations running these vulnerable versions face substantial risk of targeted attacks, especially in environments where users interact with rich media content or document editing features. The vulnerability's exploitation potential is heightened by the fact that it requires no special user interaction beyond normal browsing behavior, making it an attractive target for automated attack tools. Security researchers have noted that such use-after-free vulnerabilities often serve as stepping stones for more complex attacks, as they can be combined with other techniques to achieve persistent access or data exfiltration.
Mitigation strategies for CVE-2017-7819 primarily focus on immediate software updates and version management practices. Organizations should prioritize upgrading to Firefox 56 or later versions, Firefox ESR 52.4 or later, and Thunderbird 52.4 or later to eliminate the vulnerability. Browser vendors have implemented various memory safety enhancements in subsequent releases, including improved garbage collection mechanisms and enhanced object reference tracking. Additionally, users should disable design mode functionality when working with untrusted content and consider implementing browser hardening measures such as sandboxing and privilege separation. Network security controls including web application firewalls and content filtering systems can provide additional layers of protection by monitoring for suspicious behavior patterns associated with exploitation attempts. Regular vulnerability assessment programs should include checks for outdated browser versions, as this vulnerability represents a common target for attackers seeking to leverage known security flaws. The remediation process should also include user education regarding the risks of interacting with untrusted content and the importance of maintaining current software versions to protect against such memory safety vulnerabilities.