CVE-2026-93849
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Memory Exhaustion in Mattermost WebSocket Decoder

Publication date: 2026-10-26

Last updated on: 2026-10-26

Assigner: Mattermost, Inc.

Description
Mattermost versions 11.9.x <= 11.9.1, 11.8.x <= 11.8.5, 11.7.x <= 11.7.10, 11.10.x <= 11.10.1 Mattermost fail to apply allocation limits to the byte-string decode paths in its WebSocket msgpack decoder, which allows an authenticated remote attacker to cause excessive server memory allocation via a crafted binary WebSocket frame declaring a Bin32 payload length of up to 4,294,967,295 bytes.. Mattermost Advisory ID: MMSA-2026-00768

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Meta Information

Published
2026-10-26
Last Modified
2026-10-26
Generated
2026-10-26
AI Q&A
2026-10-26
EPSS Evaluated
N/A
NVD
CVE-2026-93849
EUVD
EUVD-2026-109937

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
Mattermost Mattermost 11.9.0
Mattermost Mattermost 11.8.0
Mattermost Mattermost 11.7.0
Mattermost Mattermost 11.10.0

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-789 The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.

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Executive Summary

This vulnerability affects Mattermost versions between 11.7.0 and 11.10.1. It involves a failure to enforce memory allocation limits in the WebSocket msgpack decoder. An authenticated remote attacker can exploit this by sending a crafted binary WebSocket frame with a falsely large payload size (up to 4,294,967,295 bytes), causing the server to allocate excessive memory.

Impact Analysis

This vulnerability can lead to denial-of-service conditions by exhausting server memory, potentially crashing the application or making it unresponsive. It requires an authenticated attacker, so unauthorized users cannot exploit it directly.

Mitigation Strategies

Upgrade Mattermost to a patched version (11.9.2 or later, 11.8.6 or later, 11.7.11 or later, or 11.10.2 or later) to address the memory allocation issue in the WebSocket msgpack decoder.

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