CVE-2016-1738

Vulnerability

A vulnerability in the dynamic linker (dyld) component of Apple OS X (before version 10.11.4) allows attackers to bypass a code-signing protection mechanism. The issue arises when handling a modified application; the integrity check intended to verify the signature of the executable before it is loaded can be circumvented. Affected versions are OS X El Capitan v10.11 through v10.11.3, as well as OS X Mavericks v10.9.5 and OS X Yosemite v10.10.5 for related code paths [1].

Exploitation

An attacker must have the ability to distribute or execute a maliciously modified application on a target system. The modified app is crafted such that dyld fails to properly verify its code signature during the loading process. No additional authentication or specific user interaction beyond launching the app is explicitly required; however, the attacker cannot rely on elevated privileges before exploitation [1]. The precise steps would involve creating a modified app binary that bypasses signature checks and then triggering its execution.

Impact

Successful exploitation allows the attacker to execute arbitrary code with the privileges of the victim user. This bypasses the intended code-signing security policy of OS X, which is designed to prevent unsigned or tampered code from running. The attacker can achieve code execution at the user level, potentially leading to further compromise of the system (e.g., data access, installation of malware) [1].

Mitigation

Apple addressed this vulnerability in OS X El Capitan v10.11.4, released on March 21, 2016. Users are strongly advised to update to 10.11.4 or later via the Mac App Store. For OS X Mavericks v10.9.5 and Yosemite v10.10.5, Apple also provided the Security Update 2016-002, which includes fixes for relevant code paths. No workarounds were published, and this CVE is not currently listed in CISA's Known Exploited Vulnerabilities catalog [1].