CVE-2017-5433 in Firefox
Summary
by MITRE
A use-after-free vulnerability in SMIL animation functions occurs when pointers to animation elements in an array are dropped from the animation controller while still in use. This results in a potentially exploitable crash. This vulnerability affects Thunderbird < 52.1, Firefox ESR < 45.9, Firefox ESR < 52.1, and Firefox < 53.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 11/26/2025
The CVE-2017-5433 vulnerability represents a critical use-after-free condition that manifests within the Simple Multimedia Integration Language animation functions of Mozilla's web browser engine. This flaw occurs when the animation controller manages pointers to animation elements within an array structure, creating a scenario where memory references become invalid while still being actively utilized by the application's execution flow. The vulnerability specifically targets the SMIL animation processing subsystem, which handles multimedia content integration and dynamic visual effects in web pages. The issue arises from improper memory management practices where the system drops references to animation elements without ensuring that all active pointers to those elements have been properly dereferenced, creating a window of opportunity for malicious exploitation. The affected software versions include Thunderbird versions prior to 52.1, Firefox Extended Support Release versions before 45.9 and 52.1, and Firefox versions before 53, indicating this vulnerability impacted a substantial portion of the Mozilla ecosystem's user base.
The technical implementation of this vulnerability stems from the fundamental flaw in how the animation controller manages memory references during the lifecycle of SMIL animation elements. When animation elements are removed from the controller's array structure, the system fails to properly invalidate all outstanding pointers to those elements before allowing the memory to be reclaimed or reused. This creates a use-after-free condition where subsequent operations on the freed memory location can trigger undefined behavior, potentially leading to memory corruption and application instability. The vulnerability operates at the intersection of memory management and multimedia processing, where the animation elements maintain references to DOM objects and rendering contexts that become invalid upon element removal. The flaw is particularly dangerous because it occurs during the processing of SMIL animations, which are commonly used in web content for creating dynamic visual effects, making exploitation possible through standard web browsing activities without requiring special privileges or user interaction beyond visiting malicious websites.
The operational impact of CVE-2017-5433 extends beyond simple application crashes to potentially enable remote code execution attacks, making it a significant security concern for affected users. Attackers can leverage this vulnerability by crafting malicious web content that triggers the specific SMIL animation processing path, causing the animation controller to drop pointers while they remain in use. The resulting memory corruption can be exploited to execute arbitrary code within the context of the affected browser application, potentially allowing attackers to gain full control over the user's system. This vulnerability aligns with the CWE-416 use-after-free weakness classification, which specifically addresses improper handling of memory references after they have been freed, and represents a classic example of how multimedia processing components can introduce security risks into browser environments. The attack surface is particularly broad since SMIL animations are supported across multiple browser versions and platforms, making the vulnerability effective against a wide range of targets and increasing its potential impact.
Mitigation strategies for CVE-2017-5433 primarily focus on immediate software updates and patches that address the underlying memory management issues in the animation controller's handling of SMIL elements. Users and organizations should prioritize updating to the patched versions of affected software, specifically Thunderbird 52.1, Firefox ESR 45.9 and 52.1, and Firefox 53 or later releases. Additionally, security-conscious administrators can implement browser hardening measures such as disabling SMIL animation support in web content processing, implementing strict content security policies that limit the execution of potentially malicious multimedia content, and deploying intrusion detection systems that monitor for exploitation attempts targeting this specific vulnerability. The ATT&CK framework categorizes this vulnerability under the T1059.007 technique for command and control communications, as exploitation may involve establishing persistent access through the compromised browser environment. Organizations should also consider implementing network-level protections such as web application firewalls and content filtering solutions that can block malicious SMIL content and reduce the attack surface for this particular vulnerability. Regular security assessments and vulnerability scanning should include verification of patched software versions to ensure complete remediation of the use-after-free condition.