CVE-2026-25780 in Mattermost
Summary
by MITRE • 03/16/2026
Mattermost versions 11.3.x <= 11.3.0, 11.2.x <= 11.2.2, 10.11.x <= 10.11.10 fail to bound memory allocation when processing DOC files which allows an authenticated attacker to cause server memory exhaustion and denial of service via uploading a specially crafted DOC file.. Mattermost Advisory ID: MMSA-2026-00581
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Analysis
by VulDB Data Team • 03/20/2026
This vulnerability exists in Mattermost server software where improper memory allocation bounds checking during DOC file processing creates a potential for memory exhaustion attacks. The flaw affects specific versions including 11.3.0 and earlier 11.3.x releases, 11.2.2 and earlier 11.2.x versions, and 10.11.10 and earlier 10.11.x versions. An authenticated attacker with valid credentials can exploit this weakness by uploading a maliciously crafted DOC file that triggers excessive memory allocation during file processing. The vulnerability stems from insufficient validation of file size parameters and memory allocation limits when handling Microsoft Word document formats, allowing the attacker to consume excessive server resources through carefully constructed file structures.
The technical implementation of this vulnerability involves the document processing pipeline where Mattermost attempts to parse and convert DOC files into a format suitable for display or further processing. When encountering specially crafted DOC files, the software fails to enforce proper memory allocation boundaries, leading to uncontrolled memory consumption. This memory exhaustion occurs during the parsing phase where the system allocates memory based on malformed file headers or embedded structures that appear to indicate much larger file sizes than actually exist. The flaw represents a classic denial of service condition where legitimate system resources become unavailable due to excessive consumption by the malicious input.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect system stability and availability for all authenticated users. An attacker can repeatedly upload such files to gradually deplete server memory resources, causing system slowdowns, application crashes, or complete service unavailability. The authentication requirement limits the scope to users with valid accounts, but this still represents a significant risk for organizations relying on Mattermost for communication and collaboration. The vulnerability can be exploited through automated scripts, making it particularly dangerous for high-traffic systems where repeated attacks can quickly overwhelm server capacity.
Security mitigations for this vulnerability should include immediate version upgrades to patched releases where available, as well as implementing file size limits and memory allocation constraints during document processing. Organizations should consider deploying content filtering solutions that can identify and block suspicious document file patterns before they reach the processing engine. Network-level protections such as rate limiting and connection pooling can help mitigate the impact of repeated attack attempts. The vulnerability aligns with CWE-129 Input Validation and CWE-772 Insufficient Resource Management, and maps to ATT&CK technique T1499.004 for Denial of Service via resource exhaustion. System administrators should also implement monitoring for unusual memory consumption patterns and establish automated alerts for potential exploitation attempts.