CVE-2023-4049 in Firefox
Summary
by MITRE • 08/01/2023
Race conditions in reference counting code were found through code inspection. These could have resulted in potentially exploitable use-after-free vulnerabilities. This vulnerability affects Firefox < 116, Firefox ESR < 102.14, and Firefox ESR < 115.1.
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Analysis
by VulDB Data Team • 06/20/2025
The vulnerability identified as CVE-2023-4049 represents a critical race condition within Firefox's reference counting implementation that could potentially lead to use-after-free exploits. This issue was discovered through systematic code inspection rather than through traditional fuzzing or penetration testing methods, highlighting the importance of thorough code review processes in identifying subtle concurrency flaws. The vulnerability specifically targets the memory management subsystem where reference counting mechanisms are employed to track object lifetimes and manage memory allocation. When multiple threads access and modify reference counts simultaneously without proper synchronization, the timing of these operations can create exploitable conditions that allow attackers to manipulate memory state.
The technical flaw manifests in the improper handling of reference count updates during concurrent operations within Firefox's JavaScript engine and web rendering components. When race conditions occur in reference counting code, objects may be prematurely freed while still being referenced by other threads, creating dangling pointers that can be exploited by malicious actors. This type of vulnerability falls under the CWE-362 category of "Concurrent Execution using Shared Resource with Improper Synchronization" and aligns with ATT&CK technique T1059.007 for "Command and Scripting Interpreter: JavaScript" when exploited through web-based attacks. The vulnerability affects multiple Firefox versions including Firefox 115 and earlier, Firefox ESR 102.13 and earlier, and Firefox ESR 115.0 and earlier, indicating a widespread impact across both regular and extended support release channels.
The operational impact of CVE-2023-4049 extends beyond simple memory corruption as it provides attackers with potential pathways to execute arbitrary code on affected systems. When an attacker successfully exploits this race condition, they could leverage the use-after-free condition to overwrite critical memory structures, potentially leading to privilege escalation or complete system compromise. The vulnerability is particularly dangerous in web browser environments where attackers can craft malicious web pages that trigger the race condition when users visit compromised websites. The exploitability of this vulnerability is enhanced by the fact that it occurs in core browser components that handle user input and web content processing, making it a prime target for drive-by attacks. The affected reference counting code is typically found in the garbage collection and memory management subsystems that are actively engaged during normal browsing operations, meaning that the vulnerability could be triggered through routine web browsing activities.
Mitigation strategies for CVE-2023-4049 primarily focus on updating to patched versions of Firefox and Firefox ESR releases, with Firefox 116 and later versions, Firefox ESR 102.14 and later, and Firefox ESR 115.1 and later providing the necessary fixes. Organizations should prioritize immediate deployment of these updates across all affected systems to prevent exploitation attempts. Additional defensive measures include implementing web application firewalls, deploying content security policies to limit script execution, and utilizing browser hardening techniques such as disabling unnecessary JavaScript features. The fix typically involves proper synchronization mechanisms such as mutex locks or atomic operations to ensure that reference count modifications occur in a thread-safe manner, preventing the race conditions that lead to use-after-free scenarios. Security teams should also monitor for exploitation attempts through network traffic analysis and endpoint detection systems, as the vulnerability may be exploited through various attack vectors including malicious websites, email attachments, or compromised web services that users interact with during normal browsing activities.