CVE-2019-8721 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-2019-8721 affects the ld64 linker component within Apple's Xcode development toolchain, representing a critical security flaw that has significant implications for software development environments. This issue specifically targets the ld64 linker which is responsible for combining object files into executable programs and shared libraries. The vulnerability stems from insufficient input validation mechanisms within the linker's processing routines, creating potential entry points for malicious actors to exploit during the compilation process. The flaw exists in versions prior to ld64-507.4 and was subsequently resolved in Xcode 11.0, indicating Apple's recognition of the severity of the issue. The vulnerability's classification aligns with CWE-121, which addresses buffer overflow conditions, and represents a classic example of how compiler and linker components can become attack vectors when proper validation mechanisms are absent.
The technical implementation of this vulnerability allows for arbitrary code execution when developers compile code without proper input validation, effectively elevating privileges to match those of the user running the compilation process. This means that any attacker who can influence the compilation environment or provide malicious input to the build system could potentially execute unauthorized code with the privileges of the user account performing the compilation. The flaw operates at the compilation stage rather than runtime, making it particularly dangerous because it can be exploited during the software development lifecycle, potentially compromising the integrity of the entire development environment. The attack vector typically involves crafting malicious input that, when processed by the vulnerable ld64 linker, triggers unintended code execution paths. This vulnerability demonstrates the critical importance of validating all inputs within development tools, as these components often operate with elevated privileges and can be targeted by attackers seeking to compromise the development infrastructure.
The operational impact of CVE-2019-8721 extends beyond simple code execution, as it represents a fundamental weakness in the software supply chain security model. When developers compile applications using vulnerable Xcode versions, they create potential backdoors or malicious code injection points that could persist in the final compiled binaries. This issue affects organizations that rely on Xcode for iOS and macOS application development, potentially exposing their entire development ecosystem to compromise. The vulnerability's exploitation requires minimal prerequisites, as it can be triggered during normal compilation activities without requiring special privileges or complex attack scenarios. From an attacker's perspective, this represents a low-hanging fruit vulnerability that can be leveraged to gain persistent access to development environments, potentially leading to more sophisticated attacks targeting production systems or other development resources.
Organizations should implement immediate mitigation strategies including updating to Xcode 11.0 or later versions that contain the patched ld64 component. System administrators should also consider implementing additional security controls around development environments, such as restricting write access to build systems and monitoring compilation activities for unusual patterns. The vulnerability highlights the importance of maintaining updated development toolchains and implementing proper input validation practices throughout the software development lifecycle. Security teams should conduct thorough assessments of their development environments to identify any systems still running vulnerable versions of Xcode or related toolchains. Additionally, organizations should consider implementing automated security scanning of compiled binaries to detect potential malicious code injection that might result from exploitation of this vulnerability. The remediation process should also include educating development teams about the importance of validating inputs and maintaining secure coding practices even within the development environment itself.