CVE-2024-29943 in Firefox
Summary
by MITRE • 03/22/2024
An attacker was able to perform an out-of-bounds read or write on a JavaScript object by fooling range-based bounds check elimination. This vulnerability affects Firefox < 124.0.1.
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Analysis
by VulDB Data Team • 04/13/2025
This vulnerability represents a critical memory safety issue in the JavaScript engine of Firefox browsers, specifically impacting versions prior to 124.0.1. The flaw resides in the optimization process known as range-based bounds check elimination which is designed to improve performance by removing redundant bounds checks in array operations. However, this optimization can be bypassed through sophisticated attacker techniques that manipulate the JavaScript object state in ways that confuse the compiler's analysis. The vulnerability is categorized under CWE-129 as an insufficient bounds checking, which directly relates to improper handling of array indices and memory access patterns. From an operational security perspective, this issue enables attackers to execute arbitrary code by leveraging out-of-bounds memory access patterns that should have been prevented by standard bounds checking mechanisms.
The technical exploitation of this vulnerability occurs when JavaScript code triggers optimizations that assume certain array bounds are safe, but an attacker can manipulate the object state to make these assumptions invalid. This creates a scenario where the bounds check elimination optimization removes necessary safety checks, allowing subsequent operations to access memory outside the intended array boundaries. The attacker can either read sensitive data from memory locations adjacent to the array or write data to arbitrary memory locations, potentially leading to privilege escalation or information disclosure. The attack vector typically involves carefully crafted JavaScript code that can manipulate array objects in a way that causes the JIT compiler to incorrectly optimize bounds checking logic. This vulnerability directly maps to techniques described in the ATT&CK framework under T1059.007 for JavaScript and T1555.003 for credential access, as successful exploitation can lead to data exfiltration and system compromise.
The impact of this vulnerability extends beyond simple memory corruption as it represents a fundamental flaw in the JavaScript engine's optimization pipeline. When exploited, the out-of-bounds read or write operations can be used to bypass modern memory protection mechanisms such as ASLR and DEP, making it particularly dangerous in contemporary security environments. The vulnerability affects not just the browser's JavaScript execution but can potentially be leveraged to compromise the entire browser sandbox, as the attacker can manipulate memory in ways that should be impossible according to standard security models. Security researchers have noted that this type of vulnerability is particularly challenging to detect and prevent because it occurs at the optimization level rather than during the basic execution flow, making it harder to identify through traditional static analysis. The fix implemented in Firefox 124.0.1 involves disabling or modifying the problematic bounds check elimination optimization, ensuring that proper bounds checking remains in place even under complex JavaScript execution scenarios. Organizations should prioritize immediate patching of affected Firefox versions and consider implementing additional browser hardening measures such as content security policies and sandboxing configurations to reduce the potential impact of similar vulnerabilities.