CVE-2021-30877 in macOS
Summary
by MITRE • 08/25/2021
An out-of-bounds read was addressed with improved bounds checking. This issue is fixed in macOS Monterey 12.0.1, Security Update 2021-007 Catalina, macOS Big Sur 11.6.1. Processing a maliciously crafted AppleScript binary may result in unexpected application termination or disclosure of process memory.
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Analysis
by VulDB Data Team • 10/31/2021
The vulnerability identified as CVE-2021-30877 represents a critical out-of-bounds read flaw within Apple's macOS operating system that affects multiple versions including macOS Big Sur 11.6.1 and earlier releases. This issue stems from inadequate bounds checking mechanisms when processing AppleScript binary files, creating a potential vector for malicious exploitation that could compromise system integrity and data confidentiality. The vulnerability specifically manifests during the parsing of crafted AppleScript binary content, where the system fails to properly validate array indices or memory boundaries before accessing data structures. This fundamental flaw in input validation allows attackers to manipulate the execution flow of applications that process AppleScript content, potentially leading to unauthorized memory access patterns that could expose sensitive information or cause application crashes.
The technical nature of this vulnerability aligns with CWE-129, which describes improper validation of array index bounds, and represents a classic example of how insufficient input sanitization can lead to memory corruption issues. When an application processes a maliciously crafted AppleScript binary, the system's failure to properly validate the bounds of data structures results in the execution attempting to read memory locations outside the intended buffer boundaries. This type of vulnerability falls under the ATT&CK technique T1059.007 for AppleScript execution, where adversaries leverage legitimate system tools to execute malicious code. The flaw specifically impacts applications that utilize AppleScript's binary format processing capabilities, including various system utilities, development tools, and third-party applications that may parse or execute AppleScript content. The out-of-bounds read condition can manifest in two primary ways: either causing the affected application to terminate unexpectedly through segmentation faults or potentially enabling information disclosure where process memory contents become accessible to unauthorized parties.
The operational impact of CVE-2021-30877 extends beyond simple application instability, as it creates potential pathways for more sophisticated attacks that could be leveraged in targeted campaigns. An attacker who successfully exploits this vulnerability could potentially cause denial of service conditions across multiple system applications that process AppleScript content, while also gaining access to sensitive memory segments that might contain authentication tokens, cryptographic keys, or other confidential information. The vulnerability's exploitation requires minimal privileges and can be executed through social engineering tactics that trick users into executing malicious AppleScript binaries, making it particularly dangerous in enterprise environments where users may inadvertently execute compromised content. The fact that this vulnerability affects multiple macOS versions including Big Sur and Catalina demonstrates the widespread nature of the issue, requiring coordinated patch management efforts across various operating system releases. Organizations must consider the potential for this vulnerability to be used as a stepping stone for more complex attacks, as memory disclosure issues often serve as precursors to privilege escalation or information gathering operations.
Mitigation strategies for CVE-2021-30877 center around immediate patch deployment and application of the security updates released by Apple for macOS Monterey 12.0.1, Security Update 2021-007 Catalina, and macOS Big Sur 11.6.1. System administrators should prioritize deployment of these updates across all affected systems to eliminate the vulnerability at its source. Additionally, organizations should implement application whitelisting policies that restrict execution of AppleScript binaries from untrusted sources, combined with monitoring for suspicious AppleScript execution patterns that might indicate exploitation attempts. Network-level protections can include implementing sandboxing measures that isolate AppleScript processing environments and employing behavioral monitoring tools that detect anomalous memory access patterns. The vulnerability's remediation requires careful attention to the specific patch versions mentioned in the advisory, as each update addresses different aspects of the underlying memory management issues. Security teams should also conduct vulnerability assessments to identify applications that may be particularly susceptible to this class of issue, focusing on those that process user-supplied AppleScript content or have extensive AppleScript integration. Regular security awareness training for users can help prevent successful exploitation through social engineering approaches that rely on user interaction with malicious AppleScript content.