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CVE-2026-26233— Denial of Service via HTTP/2 single packet attack on login endpoint

Quick assessment

Affected
Mattermost Mattermost
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.4.0及之前的11.4.x版本、11.3.1及之前的11.3.x版本、11.2.3及之前的11.2.x版本和10.11.11及之前的10.11.x版本存在安全漏洞，该漏洞源于未对登录请求进行速率限制，可能导致未经身份验证的远程攻击者通过HTTP/2单数据包攻击造成拒绝服务。

CVSS 4.3 · Medium EPSS 0.52% · P43
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I. Basic Information for CVE-2026-26233

Vulnerability Information
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Vulnerability Title
Denial of Service via HTTP/2 single packet attack on login endpoint
Source: CVE Program / CVE List V5
Vulnerability Description
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
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: CVE Program / CVE List V5
Vulnerability Title
Mattermost 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Mattermost是美国Mattermost公司的一个开源协作平台。 Mattermost 11.4.0及之前的11.4.x版本、11.3.1及之前的11.3.x版本、11.2.3及之前的11.2.x版本和10.11.11及之前的10.11.x版本存在安全漏洞，该漏洞源于未对登录请求进行速率限制，可能导致未经身份验证的远程攻击者通过HTTP/2单数据包攻击造成拒绝服务。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Mattermost Mattermost 11.4.0 ~ 11.4.0 -

II. Public POCs for CVE-2026-26233

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III. Intelligence Information for CVE-2026-26233

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Same Patch Batch · Mattermost · 2026-03-25 · 4 CVEs total

CVE-2026-27656 5.7 MEDIUM Account Takeover via Substring Matching in OpenID Connect Authentication
CVE-2026-27659 4.6 MEDIUM CSRF vulnerability in UpdateAccessControlPolicyActiveStatus endpoint
CVE-2026-20719 4.3 MEDIUM DoS via URL Previews Rendering Malicious SVGs

IV. Related Vulnerabilities

Same product: Mattermost
Same vendor: Mattermost
Same weakness: CWE-400

V. Comments for CVE-2026-26233

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