CVE-2026-10600 Overview
CVE-2026-10600 affects multiple Mattermost server versions and allows authenticated users to degrade file upload functionality for all users. The vulnerability stems from missing bounds on time and resource consumption during server-side document content extraction [CWE-770]. An authenticated user with file-upload permission can saturate the shared extraction worker pool by repeatedly uploading small documents that are cheap to submit but expensive to process. This is tracked as Mattermost Advisory ID MMSA-2026-00694.
Critical Impact
Authenticated attackers can exhaust the shared extraction worker pool, disrupting file uploads across all users on the affected Mattermost server.
Affected Products
- Mattermost 11.8.x versions up to and including 11.8.0
- Mattermost 11.7.x versions up to and including 11.7.3, and 11.6.x versions up to and including 11.6.5
- Mattermost 10.11.x versions up to and including 10.11.20
Discovery Timeline
- 2026-07-27 - CVE-2026-10600 published to NVD
- 2026-07-27 - Last updated in NVD database
Technical Details for CVE-2026-10600
Vulnerability Analysis
Mattermost performs server-side content extraction on uploaded documents to enable search indexing. The extraction process runs inside a shared worker pool bounded by the server, not by the individual request. The affected versions do not enforce time or resource limits on how long a single extraction task may consume worker capacity.
An authenticated user with file-upload permission can send many small documents crafted to be inexpensive to upload but computationally expensive to parse. Because extraction workers are shared across the entire server, these tasks starve legitimate uploads. The result is availability degradation for every user attempting to upload files while the pool is saturated.
The issue is categorized as Allocation of Resources Without Limits or Throttling [CWE-770]. The Exploit Prediction Scoring System places CVE-2026-10600 at a probability of 0.212%.
Root Cause
The root cause is missing bounds on document extraction operations. Neither per-task timeouts nor per-user quotas cap how long extraction workers spend on a single upload. Combined with a shared pool architecture, one authenticated user can consume worker capacity intended for the entire server.
Attack Vector
Exploitation requires network access and valid credentials with file-upload permission. No user interaction is needed and complexity is low. The attacker repeatedly submits small documents structured to trigger expensive parsing paths in the extraction pipeline. Refer to the Mattermost Security Updates advisory for technical detail on the affected extraction path.
Detection Methods for CVE-2026-10600
Indicators of Compromise
- Sustained high CPU or memory utilization on Mattermost extraction workers without corresponding growth in stored file volume.
- A single authenticated account submitting a high rate of small document uploads over a short window.
- User reports of failing or delayed file uploads while server processes remain healthy.
Detection Strategies
- Alert on extraction worker queue depth exceeding baseline thresholds during normal business hours.
- Correlate upload event logs with per-user upload rate to identify accounts submitting outlier volumes of documents.
- Baseline average extraction duration per document type and flag deviations that indicate expensive parsing.
Monitoring Recommendations
- Instrument the extraction worker pool with metrics for task duration, queue depth, and worker saturation.
- Ingest Mattermost application logs and worker telemetry into a centralized log platform for retention and correlation.
- Track file upload API calls per authenticated user and generate alerts when rates exceed defined thresholds.
How to Mitigate CVE-2026-10600
Immediate Actions Required
- Upgrade Mattermost servers to a fixed release as identified in the Mattermost Security Updates advisory for MMSA-2026-00694.
- Review file-upload permissions and remove the capability from accounts that do not require it.
- Enforce rate limits on file upload endpoints at a reverse proxy or API gateway.
Patch Information
Mattermost has published fixes referenced under advisory MMSA-2026-00694. Administrators should consult the Mattermost Security Updates page for the specific patched versions corresponding to the 11.8.x, 11.7.x, 11.6.x, and 10.11.x branches.
Workarounds
- Apply per-user upload rate limiting at the load balancer or web application firewall to cap document submission frequency.
- Restrict file-upload permission through Mattermost role configuration to trusted users pending upgrade.
- Monitor extraction worker health and restart the service if saturation is detected to restore upload availability.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
