Is there a public exploit for CVE-2026-71554?

Yes. Proof-of-concept code for CVE-2026-71554 has been published publicly.

Is there a proof of concept for CVE-2026-71554?

Yes — 1 proof-of-concept entry is linked on this page, from public repositories and community submissions. They are listed for authorised testing only.

How severe is CVE-2026-71554?

CVE-2026-71554 scores CVSS 5.3 (v3.1), rated medium. EPSS puts the chance of exploitation in the next 30 days at 0.42%.

What does CVE-2026-71554 affect?

CVE-2026-71554 affects python-hyper h2.

5.3 Medium

h2 is a pure-Python implementation of a HTTP/2 protocol stack.

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 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.

Proof-of-concept code is published

Public PoC

Public PoCSunandM/poc-h2-CVE-2026-715541 stars

Signals come from Exploit-DB, Metasploit, Nuclei and published proof-of-concept repositories. Their absence means nothing was found, not that nothing exists.

Assessment

CVSS: 5.3 (v3.1)
Severity: Medium
EPSS: 0.42% chance of exploitation in the next 30 days
Known exploited: Not listed in CISA KEV
Exploit availability: Public PoC
Published: 6 August 2026
Last updated: 24 October 2026
Affected: python-hyper · h2
Weakness: CWE-444
Assigner: security-advisories@github.com

CVSS vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

At the source

References

Community proofs of concept

No community proof of concept yet. If you have one for a published vulnerability and the right to share it, add it below — it will appear here once reviewed.

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