CVE-2017-2491 in Safari
Summary
by MITRE
Use after free vulnerability in the String.replace method JavaScriptCore in Apple Safari in iOS before 10.3 allows remote attackers to execute arbitrary code via a crafted web page, or a crafted file.
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Analysis
by VulDB Data Team • 01/24/2025
The CVE-2017-2491 vulnerability represents a critical use-after-free flaw within Apple Safari's JavaScriptCore engine affecting iOS versions prior to 10.3. This vulnerability specifically manifests in the String.replace method implementation, where improper memory management allows attackers to manipulate freed memory locations. The flaw arises from insufficient bounds checking and memory deallocation procedures within the JavaScript engine's string manipulation routines, creating opportunities for memory corruption that can be exploited through web-based attacks.
The technical implementation of this vulnerability involves a classic use-after-free scenario where JavaScriptCore allocates memory for string objects during replace operations, subsequently frees this memory, but fails to properly invalidate references to the freed memory region. Attackers can craft malicious web pages that trigger specific string replacement patterns, causing the JavaScript engine to execute code that operates on the freed memory space. This memory corruption can lead to arbitrary code execution with the privileges of the Safari process, effectively allowing remote attackers to compromise iOS devices through web browser exploitation.
From an operational perspective, this vulnerability presents significant risk to iOS users as it enables remote code execution through standard web browsing activities without requiring user interaction beyond visiting malicious websites. The exploitability is enhanced by the fact that JavaScriptCore is actively used in Safari's rendering engine, making this attack vector accessible through routine web browsing. The vulnerability's impact extends beyond individual device compromise to potentially enable further lateral movement within network environments where iOS devices are present, particularly in enterprise settings where mobile device management policies may be insufficient.
The attack surface for this vulnerability aligns with several ATT&CK framework techniques including T1059.007 for JavaScript execution and T1068 for local privilege escalation. According to CWE classification, this represents a CWE-416 use-after-free vulnerability that occurs when memory is freed but references remain accessible, creating opportunities for memory corruption attacks. The vulnerability demonstrates poor memory management practices within Apple's JavaScriptCore implementation, where the string replacement method does not properly track object lifetimes or validate memory access patterns after deallocation.
Mitigation strategies should prioritize immediate patching of affected iOS versions to 10.3 or later, as this represents the most effective defense against exploitation. Network administrators should implement web filtering solutions that can identify and block known malicious domains associated with exploitation attempts. Browser security enhancements including sandboxing mechanisms and strict memory access controls should be enabled to limit potential damage from successful exploitation attempts. Additionally, users should be educated about avoiding untrusted websites and maintaining current software versions to prevent exploitation of this and similar vulnerabilities in the JavaScriptCore engine.