CVE-2026-26233— Denial of Service via HTTP/2 single packet attack on login endpoint
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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: NVD (National Vulnerability Database)
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: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Source: NVD (National Vulnerability Database)
Vulnerability Type
未加控制的资源消耗(资源穷尽)
Source: NVD (National Vulnerability Database)
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
| # | POC Description | Source Link | Shenlong Link |
|---|
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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
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Connected Workspaces: Malicious remote server can manipulate - CVE-2026-24661
Unbounded Request Body Read in MS Teams Plugin {{/changes}} - CVE-2026-21388
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}
Same vendor: Mattermost
- CVE-2026-3590
Race Condition in Guest Magic Link Authentication Allows Tok - CVE-2026-28741
CSRF Protection Bypass Allows Updating a User's Authenticati - CVE-2026-27769
Connected Workspaces: Malicious remote server can manipulate - CVE-2026-24661
Unbounded Request Body Read in MS Teams Plugin {{/changes}} - CVE-2026-21388
Unbounded Request Body Read in MS Teams Plugin {{/lifecycle}
Same weakness: CWE-400
- CVE-2026-42304
Twisted: Denial of Service (DoS) in twisted.names via Crafte - CVE-2026-44248
Netty: Resource exhaustion in MqttDecoder - CVE-2026-42587
Netty: HttpContentDecompressor maxAllocation bypass via Cont - CVE-2026-42583
Netty: Lz4FrameDecoder resource exhaustion - CVE-2026-44456
Hono: bodyLimit() can be bypassed for chunked / unknown-leng
V. Comments for CVE-2026-26233
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