CVE-2015-5850 in iOS
Summary
by MITRE
AppleKeyStore in Apple iOS before 9 allows physically proximate attackers to reset the count of incorrect passcode attempts via a device backup.
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Analysis
by VulDB Data Team • 06/15/2022
The vulnerability described in CVE-2015-5850 resides within AppleKeyStore, a critical component of Apple iOS operating systems that manages cryptographic keys and passcode-related security functions. This weakness affects iOS versions prior to 9.0, creating a significant security gap that can be exploited by attackers who have physical access to a target device. The flaw specifically relates to the passcode attempt counter mechanism that is designed to protect against brute force attacks by temporarily locking the device after multiple failed authentication attempts. The vulnerability stems from insufficient validation of backup operations that can reset this critical security counter, effectively allowing attackers to bypass the built-in protection mechanisms that are meant to deter unauthorized access through repeated passcode guessing attempts.
The technical implementation of this vulnerability involves a flaw in how AppleKeyStore handles device backup operations and passcode attempt tracking. When a device backup occurs, the system should maintain the integrity of the passcode attempt counter to preserve the security posture established by the device's lockout policies. However, the flaw allows backup operations to reset this counter to zero, effectively resetting the security timer that would normally prevent further passcode attempts for a specified period. This occurs because the backup process does not properly validate whether the passcode attempt counter should be reset or maintained during backup operations, creating an attack vector that can be exploited by physically proximate adversaries who can perform backup operations on the target device.
The operational impact of this vulnerability extends beyond simple bypass of passcode security measures and represents a fundamental weakness in the device's threat model for physically proximate attacks. Attackers with physical access to an iOS device can exploit this vulnerability to repeatedly attempt passcode guessing without triggering the normal security protections that would typically lock the device after a certain number of failed attempts. This creates a scenario where an attacker can systematically work through passcode combinations without the device's built-in countermeasures being effective, significantly increasing the probability of successful unauthorized access. The vulnerability is particularly concerning because it operates at the system level where backup operations are typically considered safe and legitimate functions, making it difficult for users to detect or prevent the exploitation.
From a cybersecurity perspective, this vulnerability aligns with several common attack patterns documented in the ATT&CK framework, particularly those related to credential access and privilege escalation. The flaw enables an attacker to perform passcode brute force attacks that would normally be mitigated by device lockout mechanisms, representing a category of attacks that fall under credential stuffing and brute force techniques. The vulnerability also demonstrates poor input validation and improper state management issues that are commonly classified under CWE categories such as CWE-20 for improper input validation and CWE-362 for concurrent execution use of a resource. Security professionals should recognize this as a critical weakness that undermines the fundamental security assumptions of mobile device protection mechanisms, particularly in environments where physical access to devices cannot be guaranteed.
Mitigation strategies for this vulnerability require both immediate and long-term approaches that address both the specific flaw and broader security practices. The primary recommendation is to upgrade to iOS 9.0 or later versions where Apple has implemented proper validation of backup operations against passcode attempt counters. Organizations should also implement additional security measures such as enabling automatic device lockout policies, using strong passcodes with sufficient complexity, and implementing mobile device management solutions that can enforce additional security controls. Security teams should conduct regular assessments of device backup procedures to ensure that backup operations do not inadvertently reset critical security counters, and consider implementing monitoring solutions that can detect anomalous backup patterns that might indicate exploitation attempts. Additionally, user education regarding the importance of physical security and the risks associated with allowing unauthorized access to devices remains crucial in defending against this type of attack vector.