CVE-2018-5127 in Firefox
Summary
by MITRE
A buffer overflow can occur when manipulating the SVG "animatedPathSegList" through script. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.7, Firefox ESR < 52.7, and Firefox < 59.
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Analysis
by VulDB Data Team • 11/26/2025
The vulnerability identified as CVE-2018-5127 represents a critical buffer overflow condition within the rendering engine of Mozilla Firefox and Thunderbird applications. This flaw specifically manifests when processing Scalable Vector Graphics content that utilizes the animatedPathSegList attribute, which is part of the SVG 1.1 specification for defining animated paths in vector graphics. The issue stems from insufficient bounds checking during the manipulation of path segment lists in SVG animations, creating a scenario where maliciously crafted SVG content can trigger memory corruption. The vulnerability affects versions prior to 52.7 for Firefox ESR and Thunderbird, and before version 59 for regular Firefox releases, indicating this was a significant security gap that required immediate attention from users and administrators.
The technical implementation of this vulnerability involves the manipulation of SVG path data structures through JavaScript APIs, specifically targeting the animatedPathSegList property which allows dynamic modification of path segments in animated SVG graphics. When an application processes SVG content containing malformed or excessively large animated path segment lists, the underlying buffer allocation and memory management routines fail to properly validate input boundaries. This leads to a classic buffer overflow condition where data written beyond allocated memory boundaries can overwrite adjacent memory regions, potentially corrupting critical program state or executing arbitrary code. The flaw operates at the intersection of web standards processing and memory safety, making it particularly dangerous in the context of browser-based exploitation.
The operational impact of CVE-2018-5127 extends beyond simple application crashes, as the buffer overflow condition creates opportunities for remote code execution attacks. Attackers can craft malicious SVG files that, when loaded by vulnerable browsers, trigger the overflow during normal SVG rendering operations. This vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and can be mapped to ATT&CK technique T1059.007 for script-based exploitation. The affected applications process SVG content through multiple code paths, including the SVG rendering engine and JavaScript execution environments, making exploitation possible through various attack vectors including web pages, email attachments, or embedded content in web applications. The crash conditions resulting from this vulnerability can be leveraged to bypass security mitigations such as address space layout randomization and data execution protection mechanisms.
Mitigation strategies for CVE-2018-5127 primarily focus on immediate version updates to patched releases of Firefox and Thunderbird, which address the underlying buffer overflow through proper input validation and memory management. Organizations should prioritize patch deployment across all affected systems, particularly those handling untrusted SVG content or operating in high-risk environments. Additional protective measures include implementing content security policies that restrict SVG loading from untrusted sources, deploying web application firewalls that can detect and block malicious SVG content, and enabling sandboxing mechanisms that limit the impact of successful exploitation attempts. Security monitoring should focus on detecting unusual SVG processing patterns or memory allocation behaviors that might indicate exploitation attempts, while user education regarding the risks of opening untrusted SVG files remains crucial for overall security posture maintenance.