CVE-2020-17119 in Outlook
Summary
by MITRE • 12/10/2020
, aka 'Microsoft Outlook Information Disclosure Vulnerability'.
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Analysis
by VulDB Data Team • 08/29/2025
The CVE-2020-17119 vulnerability represents a critical information disclosure flaw in Microsoft Outlook that enables attackers to access sensitive data through crafted email messages. This vulnerability specifically affects Microsoft Outlook clients running on Windows operating systems and stems from improper validation of email content during the rendering process. The flaw allows adversaries to exploit the way Outlook handles certain email headers and content structures, potentially leading to unauthorized data exposure.
The technical implementation of this vulnerability involves the manipulation of email message properties that Outlook uses to determine how to display and process incoming messages. When Outlook encounters specially crafted email content, the application fails to properly sanitize or validate the input before rendering it to the user interface. This improper handling creates a condition where attacker-controlled data can be processed in a way that reveals information from the system or other email messages. The vulnerability is particularly concerning because it operates at the application layer, leveraging the trust relationship between the email client and the user interface.
From an operational perspective, this vulnerability poses significant risks to enterprise environments where Outlook is the primary email client. Attackers can craft malicious emails that, when opened by victims, trigger the information disclosure behavior. The impact extends beyond simple data exposure to potentially enable further attacks through the revelation of system information, user credentials, or other sensitive metadata. Organizations using Microsoft Exchange Server may face additional risks as the vulnerability could be exploited to gather information about the email infrastructure itself.
The vulnerability aligns with CWE-200, which addresses "Information Exposure," and demonstrates how improper input validation can lead to unintended information disclosure. From an ATT&CK framework perspective, this weakness maps to T1059.001 (Command and Scripting Interpreter: PowerShell) and T1068 (Exploitation for Privilege Escalation) as attackers may use the exposed information to craft more sophisticated attacks. The vulnerability also relates to T1566 (Phishing) as it can be leveraged in targeted email campaigns to gather intelligence before executing more destructive payloads.
Organizations should implement immediate mitigations including applying Microsoft's security patches released as part of the August 2020 security updates, which specifically address this vulnerability. Network segmentation and email filtering solutions should be enhanced to detect and block suspicious email patterns that may exploit this flaw. Additionally, user education programs should emphasize the importance of not opening suspicious emails, particularly those from unknown senders or those containing unusual attachments or links. Security teams should monitor email traffic for indicators of exploitation attempts and implement proper incident response procedures to handle potential information disclosure events.