Mattermost up to 10.11.11/11.2.3/11.3.1/11.4.0/11.4.x HTTP/2 resource consumption

Summaryinfo

A vulnerability classified as problematic has been found in Mattermost up to 10.11.11/11.2.3/11.3.1/11.4.0/11.4.x. This impacts an unknown function of the component HTTP2 Handler. Performing a manipulation results in resource consumption. This vulnerability was named CVE-2026-26233. The attack may be initiated remotely. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability was found in Mattermost up to 10.11.11/11.2.3/11.3.1/11.4.0/11.4.x. It has been classified as problematic. This affects some unknown processing of the component HTTP2 Handler. The manipulation with an unknown input leads to a resource consumption vulnerability. CWE is classifying the issue as CWE-400. The product does not properly control the allocation and maintenance of a limited resource, thereby enabling an actor to influence the amount of resources consumed, eventually leading to the exhaustion of available resources. This is going to have an impact on availability. The summary by CVE is:

Mattermost versions 11.4.x <= 11.4.0, 11.3.x <= 11.3.1, 11.2.x <= 11.2.3, 10.11.x <= 10.11.11 fail to rate limit login requests which allows unauthenticated remote attackers to cause denial of service (server crash and restart) via HTTP/2 single packet attack with 100+ parallel login requests.. Mattermost Advisory ID: MMSA-2025-00566

The weakness was presented by Axel Larsson and Jakob Ristner. The advisory is shared at mattermost.com. This vulnerability is uniquely identified as CVE-2026-26233 since 02/23/2026. The exploitability is told to be easy. It is possible to initiate the attack 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 10.11.12, 11.2.4, 11.3.2, 11.4.1 or 11.5.0 eliminates this vulnerability.

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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
• 11.0
• 11.1
• 11.2
• 11.2.0
• 11.2.1
• 11.2.2
• 11.2.3
• 11.3
• 11.3.0
• 11.3.1
• 11.4
• 11.4.0

License

• open-source

CPE 2.3info

• 🔒
• 🔒
• 🔒

CPE 2.2info

• 🔒
• 🔒
• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Discussion