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CVE-2026-71554: 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 eve

mediumCVSS 5.3CVE-2026-71554
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.

Details

Source
NVD Recent CVEs (US · database · site)
Severity
medium — CVSS 5.3
Published
2026-08-06
Last updated
2026-08-06
Exploitation
Not in CISA KEV at last sync

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2026-71554

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2026-71554coverage & exploitation statusNVD · CVE.org

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