CVE-2026-71554h2: Duplicate Host header could facilitate request smuggling
Updated under an hour ago ()
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It affects python-hyper h2. Add what you run to find out whether that includes you.
No exploitation reported and no EPSS estimate yet.
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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.
- CVSS
- 5.3 MEDIUM (v3.1, CNA)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
- Weakness (CWE)
- CWE-444
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- GitHub_M
- NVD analysis
- Deferred
- Record last updated
- Aug 8, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
python-hyper h2 python_hyper:h2 (from the name) | before 4.4.1 | CNA record |
References
- https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwgx-refsource-confirm
- https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6x-refsource-misc
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.