Mattermost up to 10.11.22/11.7.8/11.8.4/11.9.0 Markdown parser denial of service

Summaryinfo

A vulnerability has been found in Mattermost up to 10.11.22/11.7.8/11.8.4/11.9.0 and classified as problematic. The impacted element is an unknown function of the component Markdown parser. The manipulation leads to denial of service. This vulnerability is listed as CVE-2026-86349. The attack may be initiated remotely. There is no available exploit. The affected component should be upgraded.

Detailsinfo

A vulnerability, which was classified as problematic, has been found in Mattermost up to 10.11.22/11.7.8/11.8.4/11.9.0. This issue affects an unknown part of the component Markdown parser. The manipulation with an unknown input leads to a denial of service vulnerability. Using CWE to declare the problem leads to CWE-404. The product does not release or incorrectly releases a resource before it is made available for re-use. Impacted is availability. The summary by CVE is:

Mattermost versions 11.9.x <= 11.9.0, 11.8.x <= 11.8.4, 11.7.x <= 11.7.8, 10.11.x <= 10.11.22 fail to limit the nesting depth in the server-side Markdown parser which allows an authenticated attacker to cause a denial of service (CPU resource exhaustion) via a crafted post containing deeply nested blockquotes or list items.. Mattermost Advisory ID: MMSA-2026-00707

The advisory is shared at mattermost.com. The identification of this vulnerability is CVE-2026-86349 since 09/07/2026. The exploitation is known to be easy. The attack may be initiated remotely. Neither technical details nor an exploit are publicly available. MITRE ATT&CK project uses the attack technique T1499 for this issue.

Upgrading to version 10.11.23, 11.7.9, 11.8.5, 11.9.1 or 11.10.0 eliminates this vulnerability.

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Productinfo

Type

• Groupware Software

Name

• Mattermost

Version

• 10.11.0
• 10.11.1
• 10.11.2
• 10.11.3
• 10.11.4
• 10.11.5
• 10.11.6
• 10.11.7
• 10.11.8
• 10.11.9
• 10.11.10
• 10.11.11
• 10.11.12
• 10.11.13
• 10.11.14
• 10.11.15
• 10.11.16
• 10.11.17
• 10.11.18
• 10.11.19
• 10.11.20
• 10.11.21
• 10.11.22
• 11.0
• 11.1
• 11.2
• 11.3
• 11.4
• 11.5
• 11.6
• 11.7
• 11.7.0
• 11.7.1
• 11.7.2
• 11.7.3
• 11.7.4
• 11.7.5
• 11.7.6
• 11.7.7
• 11.7.8
• 11.8
• 11.8.0
• 11.8.1
• 11.8.2
• 11.8.3
• 11.8.4
• 11.9.0

License

• open-source

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Discussion