EUVD-2026-109838
GHSA-p4vm-rgr6-x9pc
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessAuthenticate to Mattermost instance
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DeliveryCraft Zoom chat transcript with short continuation lines
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ExploitInvoke Agents plugin to summarize transcription
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ExecutionUnvalidated line-length slice fails
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ImpactAgents plugin crashes (denial of service)
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A10:2025 - Mishandling of Exceptional Conditions
ASVS 5.0
V16 - Security Logging and Error Handling Unusual condition handling
|
| Exploitation Conditions | Exploitation requires an authenticated Mattermost account (PR:L) plus a deployment running the Agents plugin with Zoom integration enabled - the crash is reached specifically by invoking the plugin's summarization of a Zoom chat transcription. The concrete trigger is a transcription containing short continuation lines whose length is not validated before slicing. Limiting factors: authentication is required (not anonymous), the Agents plugin and Zoom chat-transcription feature must be configured/in use (not a universal default of every Mattermost install), and impact is confined to availability of the Agents plugin rather than the whole server. Beyond these stated prerequisites, the available sources do not describe further preconditions. |
| Impact | This is a moderate-severity, availability-only denial-of-service issue in the Mattermost Agents plugin (CVSS 6.5; CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H), not a high-urgency emergency. The CVSS vector indicates a network-reachable, low-complexity attack requiring low privileges (PR:L), i.e. an authenticated user, with no user interaction and no confidentiality or integrity impact - only availability (A:H), and the scope is Unchanged, meaning the impact is confined to the affected component. The vuln.today decision label is 'this_month', consistent with a serviceable-but-not-urgent DoS. No EPSS score, no CISA KEV listing, and no PoC/exploit reference were supplied, so exploitation is: no public exploit identified at time of analysis, and there is no evidence of active exploitation. The signals are internally consistent - a self-reported (by Mattermost) crash bug with no exploitation telemetry pointing to opportunistic mass-abuse. The main data gap is the version string: 'versions <=11.9 11.1.9 11.5.8 11.10.7.0' is malformed and conflates affected and fixed branches ambiguously, so exact affected/fixed boundaries should be verified against the Mattermost advisory (MMSA-2026-00723). |
| Exploit ScenarioDerived | An authenticated Mattermost user with access to the Agents plugin and Zoom integration requests a summary of a Zoom chat transcription that contains specially short continuation lines. Because the code slices chat lines without first validating their length (CWE-754, improper check for an unusual condition), the operation crashes the Agents plugin, denying that service to users. No public exploit code has been identified at the time of analysis. |
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Alert meAnalysisAIv1 – Oct 26, 2026
Denial of service in the Mattermost Agents plugin: when the plugin summarizes a Zoom chat transcription that contains very short continuation lines, it slices those lines without first validating their length, and the resulting error crashes the plugin. Mattermost versions at or below the 11.9, 11.1.9, 11.5.8 and 11.10.7.0 branch levels are affected, and an attacker needs an authenticated account (CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H) plus a deployment where the Agents plugin and its Zoom transcription summarization are actually in use; impact is limited to availability of the plugin rather than the whole server. No public exploit code has been identified at time of analysis and the issue is not listed in CISA KEV; severity is moderate (6.5) and vendor priority is this-month rather than emergency.
RemediationAI
Treat the Mattermost advisory MMSA-2026-00723 at https://mattermost.com/security-updates as the source of truth: it enumerates the affected branch levels identified here (11.9, 11.1.9, 11.5.8 and 11.10.7.0) together with the corresponding fixed releases, and those fixed builds are the primary remediation - the supplied data does not state an exact patched version number for each branch, so confirm it on the advisory before scheduling the upgrade. Where an immediate upgrade is not possible, the practical compensating control is to disable the Agents plugin entirely, which removes the vulnerable summarization path at the cost of losing all plugin functionality for users, or, if the plugin must stay enabled, to turn off the Zoom chat transcription summarization feature so attacker-supplied transcriptions never reach the unchecked slicing code, at the cost of losing that integration. Restricting who can post or invoke Zoom transcription summarization to a small trusted group reduces exposure but does not eliminate it, since the vector requires only low privileges. After any change, watch for repeated Agents plugin restarts or crashes to detect attempted triggering, and note that the crash degrades only the plugin, not the Mattermost server itself.
Affected VersionsENISA
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Technical ContextAI · show details
The flaw is classed as CWE-754 (Improper Check for Unusual or Exceptional Conditions). Mattermost's Agents plugin ingests Zoom chat transcriptions and passes them to a summarization routine that indexes into each line by position, assuming a minimum line length. A transcription containing very short continuation lines violates that assumption, the unchecked slice fails, and the plugin process terminates - an availability-only outcome with no confidentiality or integrity impact (C:N/I:N, A:H). The CPE cpe:2.3:a:mattermost:mattermost is a wildcard match, so the vendor treats the defect as shipping in the Mattermost server distribution that bundles the plugin rather than in a separately versioned component. The CVSS vector indicates a network-reachable path requiring low privileges (PR:L) and no user interaction (UI:N), which is consistent with an authenticated user driving the plugin's summarization endpoint themselves; the available sources do not describe any additional triggering preconditions beyond the presence of the plugin, the Zoom integration and a transcription with short continuation lines.
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Severity by source
AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Authenticated user triggers the crash remotely with no interaction (PR:L, AV:N, AC:L, UI:N); impact is availability-only on the plugin (C:N/I:N/A:H), scope unchanged.
Primary rating from Vendor (Mattermost).
CVSS VectorVendor: Mattermost
DescriptionCVE.org
Mattermost versions <=11.9 11.1.9 11.5.8 11.10.7.0 fail to validate Zoom chat line length before slicing which allows an authenticated attacker to crash the Agents plugin via summarizing a Zoom chat transcription containing short continuation lines. Mattermost Advisory ID: MMSA-2026-00723
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Denial of Service attacks render applications or systems unavailable by overwhelming resources or triggering failure conditions.
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