CVE-2026-6850
Crafted message attachment causes client-side denial of service via markdown parser regex backtracking in Mattermost
Description
Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658
INFO
Published Date :
July 13, 2026, 9:16 a.m.
Last Modified :
July 13, 2026, 9:16 a.m.
Remotely Exploit :
Yes !
Source :
[email protected]
Affected Products
The following products are affected by CVE-2026-6850
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | MEDIUM | 9302f53e-dde5-4bf3-b2f2-a83f91ac0eee | ||||
| CVSS 3.1 | MEDIUM | [email protected] |
Solution
- Update Mattermost to a patched version.
- Apply the vendor-provided fix.
- Validate message attachment input.
- Mitigate client-side parsing issues.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-6850.
| URL | Resource |
|---|---|
| https://mattermost.com/security-updates |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-6850 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-6850
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-6850 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-6850 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by [email protected]
Jul. 13, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'Mattermost', 'product': 'Mattermost', 'versions': [{'status': 'affected', 'version': '11.7.0', 'versionType': 'semver', 'lessThanOrEqual': '11.7.2'}, {'status': 'affected', 'version': '11.6.0', 'versionType': 'semver', 'lessThanOrEqual': '11.6.4'}, {'status': 'affected', 'version': '10.11.0', 'versionType': 'semver', 'lessThanOrEqual': '10.11.19'}, {'status': 'unaffected', 'version': '11.8.0'}, {'status': 'unaffected', 'version': '11.7.3'}, {'status': 'unaffected', 'version': '11.6.5'}, {'status': 'unaffected', 'version': '10.11.20'}], 'defaultStatus': 'unaffected'}] Added Description Mattermost versions 11.7.x <= 11.7.2, 11.6.x <= 11.6.4, 10.11.x <= 10.11.19 fail to validate the length and content of message attachment field values, which allows an authenticated attacker to cause a denial of service for all users in a channel via a post containing a specially crafted payload that triggers catastrophic backtracking in the client-side markdown parser.. Mattermost Advisory ID: MMSA-2026-00658 Added CVSS V3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Added CWE CWE-1333 Added Reference https://mattermost.com/security-updates