CVE-2018-5155 in Firefox
Summary
by MITRE
A use-after-free vulnerability can occur while adjusting layout during SVG animations with text paths. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.8, Thunderbird ESR < 52.8, Firefox < 60, and Firefox ESR < 52.8.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5155 represents a critical use-after-free flaw that manifests during SVG animation processing, specifically when text paths are manipulated within the browser rendering engine. This issue stems from improper memory management during the layout adjustment phase of Scalable Vector Graphics processing, creating conditions where freed memory locations are accessed after being deallocated. The flaw affects major web browsers including Firefox and Thunderbird, with versions prior to 52.8 ESR and 60 respectively, making it a widespread concern across multiple software ecosystems.
The technical implementation of this vulnerability resides in the browser's SVG rendering pipeline where text path animations trigger memory allocation and deallocation sequences that fail to properly synchronize access to shared memory resources. When the layout engine processes animated SVG elements with text paths, it allocates memory for temporary rendering structures and subsequently frees this memory during animation frame updates. However, if the animation continues to reference these freed memory locations, the system experiences undefined behavior that can lead to memory corruption and potential code execution. This pattern aligns with CWE-416, which specifically addresses use-after-free vulnerabilities where memory is accessed after it has been freed, and represents a classic example of heap corruption that can be exploited by malicious actors.
The operational impact of CVE-2018-5155 extends beyond simple browser instability, as the vulnerability can be leveraged to execute arbitrary code on affected systems. Attackers can craft malicious SVG content that triggers the specific conditions leading to memory corruption, potentially allowing remote code execution with the privileges of the browser process. This exploitation capability places the vulnerability in the ATT&CK framework under the T1059.007 technique category, which covers scripting languages and the execution of malicious code through web-based attacks. The vulnerability's widespread impact across Firefox and Thunderbird versions means that a significant portion of users could be exposed to potential exploitation, particularly through phishing attacks or compromised websites that deliver malicious SVG content.
Mitigation strategies for CVE-2018-5155 primarily focus on immediate software updates to patched versions where the memory management issues have been resolved through proper synchronization of memory allocation and deallocation processes. Organizations should prioritize updating to Firefox 60 or Thunderbird 52.8 ESR releases, which contain the necessary fixes for the use-after-free conditions. Additionally, browser hardening measures such as implementing strict memory access controls, enabling sandboxing mechanisms, and deploying content security policies can provide additional defense-in-depth layers against exploitation attempts. Security teams should also monitor for any emerging variants or related vulnerabilities in the SVG rendering pipeline that might exploit similar memory management flaws, as this class of vulnerability often indicates broader issues within the browser's memory handling architecture.