Mattermost: Uncontrolled Resource Consumption
CVE-2026-5308 is a high-severity uncontrolled resource consumption vulnerability in Mattermost, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected Mattermost versions: 11.6.0 and earlier; 11.5.0 through 11.5.3; 11.4.0 through 11.4.4, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.25% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Mattermost Server to 10.11.15 or 11.4.5 or 11.5.4 or 11.6.1, whichever matches your release line, or a later version.
- Read the advisory on mattermost.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Mattermost | Mattermost | 11.6.0 and earlier; 11.5.0 through 11.5.3; 11.4.0 through 11.4.4; 10.11.0 through 10.11.14 | Not stated |
| Mattermost | Mattermost Server | 10.11.0 up to, but not including, 10.11.15; 11.4.0 up to, but not including, 11.4.5; 11.5.0 up to, but not including, 11.5.4; 11.6.0 up to, but not including, 11.6.1 | 10.11.15, 11.4.5, 11.5.4, 11.6.1 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 4.9 | Medium | CNA (mattermost.com) |
| CVSS 3.1 | 7.5 | High | NVD |
Official description
Mattermost versions 11.6.x <= 11.6.0, 11.5.x <= 11.5.3, 11.4.x <= 11.4.4, 10.11.x <= 10.11.14 fail to enforce request body size limits on plugin HTTP endpoints which allows an attacker to cause a denial of service via crafted oversized HTTP requests.. Mattermost Advisory ID: MMSA-2026-00646
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Uncontrolled Resource Consumption
The product does not properly control the allocation and maintenance of a limited resource.
How developers prevent this class of flaw
- Ensure that protocols have specific limits of scale placed on them.
- Ensure that all failures in resource allocation place the system into a safe posture.
More Uncontrolled Resource Consumption vulnerabilities (CWE-400)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Other vulnerabilities in Mattermost
- 8.0 High severity
- 7.1 High severity
- 9.3 Critical severity
- 7.1 High severity
Recent Uncontrolled Resource Consumption vulnerabilities
- 7.5 High severity
- 7.5 High severity
Microsoft Defender Denial of Service Exploited
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
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