CVE-2020-9823 in iOS
Summary
by MITRE
This issue was addressed with improved checks. This issue is fixed in iOS 13.5 and iPadOS 13.5. Users removed from an iMessage conversation may still be able to alter state.
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Analysis
by VulDB Data Team • 10/20/2020
The vulnerability described in CVE-2020-9823 represents a significant security flaw in Apple's iMessage implementation that persisted across iOS and iPadOS versions prior to 13.5. This issue stems from inadequate access control mechanisms within the messaging system, specifically affecting how the platform handles user permissions and conversation state management. The flaw allows for unauthorized modification of conversation state information, creating a persistent security risk for users who have been removed from iMessage groups or conversations. The vulnerability manifests when the system fails to properly enforce removal permissions, enabling former participants to maintain access to conversation metadata and potentially manipulate shared state information. This represents a critical failure in the principle of least privilege and proper access delegation within Apple's messaging architecture.
The technical implementation of this vulnerability involves a weakness in the permission validation process that occurs when users are removed from iMessage conversations. When a user is removed from a group conversation, the system should immediately revoke all access rights and update the conversation state to reflect the new participant list. However, the flaw allows the removed user to retain certain capabilities to modify conversation state information, effectively bypassing the intended access controls. This issue falls under the category of improper access control as defined by CWE-285, where the system fails to properly enforce access restrictions for removed participants. The vulnerability specifically impacts the conversation state management system, allowing attackers to modify metadata such as read status indicators, message timestamps, or other conversation attributes that should be immutable once a user is removed.
The operational impact of this vulnerability extends beyond simple privacy concerns to encompass potential data integrity threats and messaging manipulation. Former participants could alter conversation state information, potentially creating false read receipts, modifying message timestamps, or otherwise corrupting the conversation history in ways that could mislead other participants. This capability could be exploited for social engineering attacks, where malicious actors might manipulate conversation state to create false impressions about message delivery or read status. The vulnerability also poses risks to enterprise environments where iMessage is used for business communications, as it could enable unauthorized modification of critical communication metadata. From an attacker perspective, this represents a persistent backdoor that could be exploited for extended periods, as the vulnerability remains active until the affected iOS versions are updated.
Mitigation strategies for CVE-2020-9823 require immediate deployment of iOS 13.5 and iPadOS 13.5 updates, which address the underlying access control implementation issues. Organizations should implement comprehensive patch management procedures to ensure all affected devices receive the necessary updates promptly. Network administrators should monitor for potential exploitation attempts through unusual messaging patterns or state modifications that might indicate attempted exploitation of this vulnerability. The fix implemented by Apple addresses the core issue through enhanced validation checks that properly enforce user removal from conversations and ensure that conversation state information cannot be modified by removed participants. Security teams should also consider implementing additional monitoring for iMessage conversations to detect anomalous behavior that might indicate exploitation attempts. This vulnerability aligns with ATT&CK technique T1566, which covers social engineering through messaging systems, as it enables attackers to manipulate conversation state information to deceive other participants. The remediation process should include verification that the updated systems properly enforce access controls and that removed users cannot modify conversation state information.