CVE-2019-8724 in Xcode
Summary
by MITRE
Multiple issues in ld64 in the Xcode toolchains were addressed by updating to version ld64-507.4. This issue is fixed in Xcode 11.0. Compiling code without proper input validation could lead to arbitrary code execution with user privilege.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2019-8724 affects the ld64 linker component within Apple's Xcode toolchain, representing a critical security flaw that could enable remote code execution under specific conditions. This issue resides in the ld64 linker which is responsible for combining object files into executable binaries during the compilation process. The vulnerability specifically impacts developers who compile code using Xcode versions prior to 11.0, where the ld64 component lacks proper input validation mechanisms. According to the Common Weakness Enumeration framework, this vulnerability maps to CWE-121, which describes heap-based buffer overflow conditions, and CWE-787, which addresses out-of-bounds write errors that occur when a buffer is written to with an index that is out of bounds. The flaw manifests when the linker processes malformed input data during the compilation phase, creating opportunities for attackers to inject malicious code that executes with the privileges of the user compiling the code.
The technical implementation of this vulnerability stems from insufficient validation of input parameters within the ld64 linker's parsing routines. When processing object files or linking directives, the tool fails to properly validate the size and structure of incoming data, leading to potential memory corruption scenarios. This allows an attacker who can influence the compilation process to craft malicious input that triggers buffer overflows or memory corruption conditions. The vulnerability's exploitability is enhanced by the fact that it operates during the legitimate compilation process, making detection more challenging. From an adversarial perspective, this flaw aligns with ATT&CK technique T1059.001, which involves executing malicious code through command-line interfaces, and T1027, which covers obfuscation techniques. The attack vector typically involves a malicious actor providing specially crafted source code or object files that, when processed by the vulnerable ld64 linker, result in code execution with user privileges. This represents a privilege escalation scenario where the attacker leverages the compilation environment to execute arbitrary code.
The operational impact of CVE-2019-8724 extends beyond simple code execution, as it affects the entire software development lifecycle within environments using affected Xcode versions. Developers working in potentially compromised environments may unknowingly introduce malicious code into their projects, creating supply chain security risks. Organizations that rely on Xcode for iOS and macOS application development face significant exposure, particularly those with less stringent code review processes or those developing applications for distribution through official app stores. The vulnerability's severity is compounded by the fact that it can be exploited without requiring network connectivity or user interaction, as it operates purely within the local compilation environment. Security professionals should consider this vulnerability as part of broader application security assessments, particularly when evaluating the security posture of development environments and build servers. The flaw's presence in Xcode versions prior to 11.0 means that organizations with legacy development setups may remain exposed even after patching their end-user applications, as the underlying toolchain remains vulnerable. This vulnerability demonstrates the critical importance of keeping development toolchains updated and maintaining proper security hygiene throughout the software development lifecycle.
The recommended mitigation strategy centers on immediate upgrading to Xcode 11.0 or later versions where the ld64 component has been patched to address the input validation deficiencies. Organizations should implement automated patch management processes to ensure all development environments remain current with security updates. Additionally, developers should exercise heightened caution when compiling code from untrusted sources, implementing comprehensive code review processes and static analysis tools to detect potential malicious input patterns. Security teams should monitor for signs of exploitation attempts within their development environments and consider implementing sandboxing measures for compilation processes. The vulnerability's resolution through ld64-507.4 update demonstrates the importance of maintaining current toolchain versions and the potential security implications of using outdated development environments. Regular security assessments of development infrastructure should include evaluation of toolchain versions and their associated vulnerabilities to prevent similar issues from affecting operational security.