CVE-2026-10600 in Mattermost
Summary
by MITRE • 07/27/2026
Mattermost versions 11.8.x <= 11.8.0, 11.7.x <= 11.7.3, 11.6.x <= 11.6.5, 10.11.x <= 10.11.20 fail to bound the time and resource consumption of server-side document content extraction which allows an authenticated user with file-upload permission to degrade file uploads for all users on the server via repeatedly uploading small documents that are cheap to upload but expensive to extract, saturating the shared extraction worker pool.. Mattermost Advisory ID: MMSA-2026-00694
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Analysis
by VulDB Data Team • 07/27/2026
This vulnerability represents a sophisticated resource exhaustion attack targeting Mattermost's document processing capabilities through a carefully crafted denial of service vector. The flaw exists in server-side content extraction mechanisms that fail to properly bound computational resources during document analysis, creating a scenario where authenticated users can systematically degrade system performance for all other users. The vulnerability affects multiple version streams including 11.8.x, 11.7.x, 11.6.x, and 10.11.x, indicating this is a persistent architectural issue that has remained unaddressed across several release cycles.
The technical implementation of this vulnerability exploits the shared extraction worker pool mechanism within Mattermost's document processing architecture. When users upload documents, the system automatically attempts to extract text content from these files for indexing and search capabilities. However, the extraction process lacks proper time and resource constraints, allowing malicious actors to repeatedly upload small files that appear innocuous during upload but require substantial computational resources during extraction. This creates a scenario where the worker pool becomes saturated with expensive operations while maintaining low bandwidth usage during the initial upload phase.
From an operational perspective this vulnerability poses significant risk to enterprise deployments where Mattermost serves as a primary communication platform for organizations. The attack vector requires only authenticated access with file-upload permissions, which is commonly granted to regular users in typical deployment scenarios. Once exploited, the degradation affects all users on the server as the shared extraction worker pool becomes overwhelmed with resource-intensive operations. This creates cascading performance issues that can render the entire system unusable for document processing activities while maintaining basic communication functionality.
The vulnerability aligns with CWE-400 (Uncontrolled Resource Consumption) and demonstrates characteristics of a resource exhaustion attack pattern commonly referenced in ATT&CK framework under T1499.004 (Endpoint Denial of Service). The attack methodology specifically targets the worker pool pattern, where multiple concurrent operations consume disproportionate resources relative to their initial upload cost. This represents a classic case of computational complexity mismatch where the processing overhead grows exponentially compared to the input size during content extraction phases.
Organizations should implement immediate mitigations including limiting concurrent document extraction operations, implementing per-user resource quotas for extraction activities, and establishing proper time-bound execution limits for content processing tasks. Network-level rate limiting should be configured to prevent excessive file upload attempts within short time windows. Additionally, system administrators should monitor worker pool utilization metrics and implement automated alerting for unusual resource consumption patterns that may indicate exploitation attempts.
The root cause analysis reveals a fundamental architectural flaw in how Mattermost handles asynchronous processing of user-uploaded content. The system fails to implement proper resource governance mechanisms during the document extraction phase, allowing any authenticated user to manipulate the shared processing resources through strategic file upload patterns. This design oversight creates a persistent attack surface that can be exploited by both malicious insiders and external attackers who gain legitimate access to user accounts with appropriate permissions.
Security teams should prioritize this vulnerability in their assessment cycles as it represents a significant risk to system availability and user experience. The mitigation strategies should include implementing proper resource limits for extraction processes, establishing monitoring for anomalous upload patterns, and ensuring that the extraction worker pool operates within defined computational boundaries. Regular security testing should validate that these controls effectively prevent the resource exhaustion scenario described in the vulnerability.
This vulnerability demonstrates the importance of considering resource consumption patterns during system design phases, particularly when implementing asynchronous processing workflows. The lack of proper bounds on computational resources during content extraction creates a dangerous attack surface that can be exploited by users with minimal privileges. Organizations using Mattermost should conduct thorough security reviews of their document processing workflows and implement appropriate safeguards to prevent similar issues in other components of their communication infrastructure.