CVE-2021-37865 in Mattermost
Summary
by MITRE • 01/18/2022
Mattermost 6.2 and earlier fails to sufficiently process a specifically crafted GIF file when it is uploaded while drafting a post, which allows authenticated users to cause resource exhaustion while processing the file, resulting in server-side Denial of Service.
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Analysis
by VulDB Data Team • 01/20/2022
The vulnerability identified as CVE-2021-37865 affects Mattermost versions 6.2 and earlier, specifically targeting the file upload and processing mechanisms within the platform's post drafting functionality. This issue represents a critical security flaw that enables authenticated attackers to exploit server-side resource exhaustion through carefully crafted malicious GIF files. The vulnerability stems from insufficient input validation and processing controls when handling image files during the draft post creation process, creating a pathway for malicious actors to consume excessive system resources.
The technical flaw manifests when the Mattermost server processes a specifically crafted GIF file uploaded during post drafting operations. The system fails to adequately validate or limit the resource consumption associated with processing these particular image files, allowing attackers to upload files that trigger excessive memory allocation and processing cycles. This improper handling creates a condition where the server's CPU and memory resources become consumed at an unsustainable rate, leading to service disruption and potential system instability. The vulnerability operates within the context of the application's file processing pipeline, where image files are analyzed for display purposes without sufficient resource constraints or validation mechanisms.
From an operational impact perspective, this vulnerability enables authenticated users to execute server-side denial of service attacks against Mattermost instances. The resource exhaustion occurs during the file processing phase, which can affect the entire server's performance and availability. Attackers can leverage this weakness to degrade system performance, potentially causing legitimate users to experience service interruptions or complete unavailability of the platform. The impact extends beyond simple service disruption as the excessive resource consumption can affect other services running on the same server infrastructure, creating cascading effects throughout the organization's communication systems.
The vulnerability aligns with CWE-400, which addresses unrestricted resource consumption, and demonstrates characteristics consistent with the ATT&CK technique T1499.004 for network denial of service attacks. Organizations utilizing Mattermost versions prior to 6.3 should prioritize immediate remediation through official patches provided by the vendor. The recommended mitigation strategy involves upgrading to Mattermost 6.3 or later versions where the file processing validation has been enhanced. Additionally, implementing upload size limits, file type restrictions, and resource monitoring mechanisms can provide additional defense-in-depth measures. Network segmentation and access controls should also be reviewed to limit the potential impact of authenticated exploitation, as the vulnerability requires valid user credentials to be leveraged effectively.