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CVE-2026-33555

Quick assessment

Affected
HAProxy HAProxy
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.

HAProxy是法国HAProxy公司的一款开源的TCP/HTTP负载均衡服务器。该服务器提供4层、7层代理，并能支持上万级别的连接，具有高效、稳定等特点。 HAProxy 3.3.6之前版本存在安全漏洞，该漏洞源于HTTP/3解析器未检查接收到的正文长度是否与先前宣布的内容长度匹配，可能导致请求夹带攻击。

CVSS 4.0 · Medium EPSS 0.58% · P45

Possible ATT&CK Techniques 1 AI

T1155
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I. Basic Information for CVE-2026-33555

Vulnerability Information
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Vulnerability Title
N/A
Source: CVE Program / CVE List V5
Vulnerability Description
An issue was discovered in HAProxy before 3.3.6. The HTTP/3 parser does not check that the received body length matches a previously announced content-length when the stream is closed via a frame with an empty payload. This can cause desynchronization issues with the backend server and could be used for request smuggling. The earliest affected version is 2.6.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:L/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
长度参数不一致性处理不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
HAProxy 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
HAProxy是法国HAProxy公司的一款开源的TCP/HTTP负载均衡服务器。该服务器提供4层、7层代理，并能支持上万级别的连接，具有高效、稳定等特点。 HAProxy 3.3.6之前版本存在安全漏洞，该漏洞源于HTTP/3解析器未检查接收到的正文长度是否与先前宣布的内容长度匹配，可能导致请求夹带攻击。
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
HAProxy HAProxy 2.6 ~ 3.3.6 -

II. Public POCs for CVE-2026-33555

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III. Intelligence Information for CVE-2026-33555

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Patches & Fixes for CVE-2026-33555 (1)

Vendor Pages for CVE-2026-33555 (1)

IV. Related Vulnerabilities

Same product: HAProxy
Same vendor: HAProxy
Same weakness: CWE-130

V. Comments for CVE-2026-33555

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