CVE-2019-9795 in Firefox
Summary
by MITRE
A vulnerability where type-confusion in the IonMonkey just-in-time (JIT) compiler could potentially be used by malicious JavaScript to trigger a potentially exploitable crash. This vulnerability affects Thunderbird < 60.6, Firefox ESR < 60.6, and Firefox < 66.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 09/07/2023
The vulnerability identified as CVE-2019-9795 represents a critical type-confusion issue within the IonMonkey just-in-time compiler component of Mozilla's JavaScript engine. This flaw exists in the complex interaction between the JIT compiler's optimization processes and JavaScript type handling mechanisms, creating a potential pathway for remote code execution through maliciously crafted JavaScript code. The vulnerability specifically impacts Firefox browser versions prior to 66 and Firefox ESR versions prior to 60.6, as well as Thunderbird versions before 60.6, making it a widespread concern across Mozilla's product ecosystem.
The technical root cause of this vulnerability lies in how IonMonkey handles type information during runtime optimization, where the compiler incorrectly manages type transitions and memory layout assumptions for JavaScript objects. When the JIT compiler encounters certain JavaScript code patterns, it may improperly infer object types or fail to properly validate type consistency, leading to situations where memory operations occur against objects with unexpected layouts. This type-confusion scenario can result in memory corruption that manifests as unpredictable crashes or potentially exploitable conditions. The vulnerability operates at the intersection of compiler optimization and memory safety, making it particularly dangerous as it can be triggered through standard web browsing activities without requiring any special privileges or user interaction beyond visiting a malicious website.
The operational impact of CVE-2019-9795 extends beyond simple browser crashes, as the type-confusion conditions can potentially be leveraged to execute arbitrary code on affected systems. Attackers could craft malicious JavaScript payloads that specifically target the IonMonkey compiler's handling of type information, potentially leading to privilege escalation or full system compromise. The vulnerability's exploitability is enhanced by the fact that it can be triggered through web content without requiring user interaction, making it particularly dangerous in phishing campaigns or drive-by download scenarios. Security researchers have classified this as a high-severity vulnerability due to its potential for remote code execution and the widespread use of affected browser versions across enterprise and consumer environments.
Mitigation strategies for CVE-2019-9795 primarily focus on immediate version updates to patched releases of Firefox, Thunderbird, and Firefox ESR. Organizations should prioritize deployment of patches for versions 60.6 and 66 respectively, as these releases contain fixes that address the type-confusion conditions in IonMonkey. Additional protective measures include implementing content security policies, disabling JavaScript in trusted environments where possible, and deploying web application firewalls that can detect and block suspicious JavaScript patterns. The vulnerability aligns with CWE-129, which addresses improper handling of length parameters, and relates to ATT&CK technique T1059.007 for JavaScript-based execution, making it a significant concern for organizations implementing security controls against browser-based attacks. Regular security monitoring and vulnerability scanning should be implemented to ensure all affected systems are properly patched and to detect any potential exploitation attempts.