CVE-2023-2793 in Server
Summary
by MITRE • 06/16/2023
Mattermost fails to validate links on external websites when constructing a preview for a linked website, allowing an attacker to cause a denial-of-service by a linking to a specially crafted webpage in a message.
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Analysis
by VulDB Data Team • 07/14/2023
The vulnerability identified as CVE-2023-2793 affects the Mattermost collaboration platform, specifically impacting its web link preview functionality. This issue stems from inadequate input validation mechanisms within the application's handling of external URLs. When users share links within Mattermost channels, the platform automatically generates previews by fetching content from the referenced websites. The flaw occurs during this automated preview generation process where the system fails to properly sanitize or validate the content of external webpages before rendering them as previews.
The technical implementation of this vulnerability allows attackers to craft malicious webpages that, when linked within Mattermost messages, can trigger unexpected behavior in the preview generation system. This occurs because Mattermost does not employ sufficient validation controls to ensure that external content conforms to expected parameters or does not contain elements designed to consume excessive system resources. The lack of proper sanitization means that specially crafted HTML, JavaScript, or other web content can be executed or processed in ways that exhaust computational resources or cause the preview generation service to hang or crash. This represents a classic denial-of-service scenario where legitimate users cannot access or generate previews for valid links due to the system being overwhelmed by malicious content.
From an operational impact perspective, this vulnerability compromises the availability and reliability of Mattermost's link preview feature, which is a core user experience element. When exploited, it can render the entire preview functionality unusable for extended periods, affecting team communication and collaboration workflows. The attack vector is particularly concerning because it requires minimal technical expertise to execute, as attackers only need to craft a malicious webpage and share the link within a Mattermost channel. This vulnerability also creates potential for broader system instability, as the preview generation service may become unresponsive or consume excessive memory and processing power, affecting other platform operations.
Security professionals should note that this vulnerability aligns with CWE-20, which addresses "Improper Input Validation," and demonstrates how insufficient validation of external inputs can lead to system instability. The issue also relates to ATT&CK technique T1499.004, "Endpoint Denial of Service," as it enables attackers to disrupt service availability through crafted content. Organizations using Mattermost should implement immediate mitigations including rate limiting for preview generation requests, implementing more robust content validation mechanisms, and potentially disabling external link previews in high-security environments. Additionally, regular security updates and monitoring of user-generated content for suspicious link patterns should be implemented as part of comprehensive defensive measures against this and similar vulnerabilities.