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CVE-2026-71554— h2: Duplicate Host header could facilitate request smuggling

Quick assessment

Affected
python-hyper h2
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.

python-hyper h2是python-hyper组织的一款支持HTTP/2协议的服务器设备。 python-hyper h2 4.4.0及之前版本存在输入验证错误漏洞，该漏洞源于接受包含多个Host标头的请求头块，并将所有Host标头转发给消费应用程序，当消费者将HTTP/2降级为HTTP/1.1时，生成的请求携带两行Host标头，可能导致请求走私。

CVSS 5.3 · Medium EPSS 0.42% · P36

Affected Version Matrix 1

VendorProduct Version RangeStatus
python-hyper h2 < 4.4.1 affected
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I. Basic Information for CVE-2026-71554

Vulnerability Information
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Vulnerability Title
h2: Duplicate Host header could facilitate request smuggling
Source: CVE Program / CVE List V5
Vulnerability Description
h2 is a pure-Python implementation of a HTTP/2 protocol stack. Versions up to and including 4.4.0 accept request header blocks containing more than one Host header, and forward every Host header to the consuming application. Where the consumer downgrades HTTP/2 to HTTP/1.1, the resulting request carries two Host header lines, providing a request smuggling primitive. This issue is fixed in version 4.4.1.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
HTTP请求的解释不一致性(HTTP请求私运)
Source: CVE Program / CVE List V5
Vulnerability Title
python-hyper h2 输入验证错误漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
python-hyper h2是python-hyper组织的一款支持HTTP/2协议的服务器设备。 python-hyper h2 4.4.0及之前版本存在输入验证错误漏洞，该漏洞源于接受包含多个Host标头的请求头块，并将所有Host标头转发给消费应用程序，当消费者将HTTP/2降级为HTTP/1.1时，生成的请求携带两行Host标头，可能导致请求走私。
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
python-hyper h2 < 4.4.1 -

II. Public POCs for CVE-2026-71554

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III. Intelligence Information for CVE-2026-71554

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Patches & Fixes for CVE-2026-71554 (1)

Vendor Advisories for CVE-2026-71554 (1)

IV. Related Vulnerabilities

Same product: h2
Same vendor: python-hyper
Same weakness: CWE-444