CVE-2020-1903 in WhatsApp
Summary
by MITRE • 10/06/2020
An issue when unzipping docx, pptx, and xlsx documents in WhatsApp for iOS prior to v2.20.61 and WhatsApp Business for iOS prior to v2.20.61 could have resulted in an out-of-memory denial of service. This issue would have required the receiver to explicitly open the attachment if it was received from a number not in the receiver's WhatsApp contacts.
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Analysis
by VulDB Data Team • 11/17/2020
The vulnerability CVE-2020-1903 represents a critical denial of service flaw affecting WhatsApp for iOS and WhatsApp Business for iOS versions prior to 2.20.61. This issue emerged from the improper handling of compressed document formats including docx, pptx, and xlsx files during the unzipping process within the mobile messaging application. The vulnerability specifically targeted the memory management mechanisms employed by WhatsApp when processing these Microsoft Office document formats that are commonly distributed as zip archives containing multiple files and metadata. The flaw exploited a fundamental weakness in how the application allocated and managed memory resources when decompressing these particular file types, creating a scenario where maliciously crafted documents could trigger excessive memory consumption.
The technical implementation of this vulnerability stems from insufficient input validation and memory allocation controls during the document extraction process. When WhatsApp for iOS encountered these compressed document attachments, the application would attempt to unzip the contents without adequate memory boundary checks or resource limiting mechanisms. This behavior aligns with CWE-129, Input Validation and Representation, and CWE-770, Allocation of Resources Without Limits or Throttling, which specifically address improper resource management and validation issues. The vulnerability operates under the principle that the application fails to properly constrain memory usage during decompression operations, allowing an attacker to craft documents that consume excessive system resources. The flaw manifests as an out-of-memory condition that can cause the application to crash or become unresponsive, effectively preventing legitimate communication through the messaging platform.
The operational impact of CVE-2020-1903 extends beyond simple service disruption to encompass broader security implications for mobile communication platforms. The vulnerability requires specific conditions to be exploited, as the malicious document must be received from a number not in the recipient's contacts, indicating a targeted attack vector that could be leveraged for social engineering campaigns. This requirement suggests that attackers would need to establish trust relationships with targets through social manipulation or other means before executing the attack. The attack pattern aligns with ATT&CK technique T1204.002, User Execution: Malicious File, as it relies on the user explicitly opening the attachment to trigger the vulnerability. The impact affects both personal and business communication channels, potentially disrupting critical business operations when WhatsApp Business applications are compromised. The vulnerability demonstrates how seemingly benign file handling operations can become security threats when proper resource management controls are absent.
Mitigation strategies for CVE-2020-1903 focus on immediate software updates and implementation of defensive measures within mobile application environments. The primary and most effective solution involves updating to WhatsApp for iOS version 2.20.61 or later, which includes proper memory management controls and input validation for document decompression operations. Organizations should implement comprehensive patch management procedures to ensure all mobile devices running WhatsApp are updated promptly. Additionally, security teams should consider implementing network-level controls that can detect and block suspicious document attachments, particularly those from untrusted sources. The vulnerability highlights the importance of proper resource allocation controls in mobile applications and demonstrates the necessity of implementing robust input validation mechanisms. Organizations should also consider implementing user education programs to raise awareness about the risks of opening attachments from unknown contacts, reinforcing the principle that mobile security requires both technical controls and user awareness. The fix implemented by WhatsApp addresses the core memory management issue through improved resource allocation and validation controls, preventing the excessive memory consumption that previously led to denial of service conditions.