CVE-2026-71554

MEDIUMPre-NVD 5.35.3—
EchelonGraph scoreMEDIUM confidence

This medium-severity CVE scores 5.3 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 62% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
5.3EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.3Exploit: None knownExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
5.3
EG Score
5.3(medium)
EG Risk
39(Track)
EG Risk 39/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity53% × 45%
Exploitation0% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
38%
KEV
Not listed

Published

August 6, 2026

Last Modified

September 18, 2026

Advisory Details (2)

Auto-updated Aug 6, 2026
Patch available. Sources: github_commit, github.
github Patch Available

Duplicate Host header could facilitate request smuggling · Advisory · python-hyper/h2 · GitHub

Affected: v4.4.1

https://github.com/python-hyper/h2/security/advisories/GHSA-6hr6-w5qg-qmwg
github_commit

commit 292a40829fee (python-hyper/h2)

Fix landed in python-hyper/h2 commit 292a40829fee — awaiting tagged release

https://github.com/python-hyper/h2/commit/292a40829feefda98c8509dcdbbb4a57af9bd6a6

Vendor Advisories for CVE-2026-71554(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Affected Packages

(5 across 5 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
python-h24.0.0-3 ... 4.3.0-2 (9 versions)——
Debian:12(1)
PackageVulnerable rangeFixed inDependents
python-h24.1.0-4, 4.2.0-1, 4.3.0-1, 4.3.0-2——
Debian:13(1)
PackageVulnerable rangeFixed inDependents
python-h24.2.0-1, 4.3.0-1, 4.3.0-2——
Debian:14(1)
PackageVulnerable rangeFixed inDependents
python-h24.2.0-1, 4.3.0-1, 4.3.0-2——
PyPI(1)
PackageVulnerable rangeFixed inDependents
h20.1.0 ... 4.4.0 (47 versions)4.4.1—

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 12× in last 7d / 45× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 20:35 UTCEG score recompute
  2. 2026-09-18 19:28 UTCEPSS rescore
  3. 2026-09-18 06:45 UTCEG score recompute
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  1. 2026-09-02 00:48 UTCEG score recompute
  2. 2026-09-01 13:54 UTCEPSS rescore
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  5. 2026-08-30 19:17 UTCEPSS rescore
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  22. 2026-08-19 17:04 UTCEPSS rescore
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  24. 2026-08-18 13:49 UTCEPSS rescore
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  26. 2026-08-17 20:44 UTCEG score recompute
  27. 2026-08-17 13:47 UTCEPSS rescore
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  29. 2026-08-16 14:56 UTCEPSS rescore
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  32. 2026-08-15 16:45 UTCEG score recompute
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  35. 2026-08-13 22:00 UTCEPSS rescore
  36. 2026-08-13 12:55 UTCEG score recompute
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  38. 2026-08-12 11:01 UTCEG score recompute
  39. 2026-08-11 09:05 UTCEG score recompute
  40. 2026-08-11 00:00 UTCEPSS rescore
  41. 2026-08-10 07:11 UTCEG score recompute
  42. 2026-08-09 13:47 UTCEPSS rescore
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  44. 2026-08-08 16:37 UTCEPSS rescore
  45. 2026-08-08 03:22 UTCEG score recompute
  46. 2026-08-08 02:52 UTCEG score recompute
  47. 2026-08-08 00:32 UTCEG score recompute
  48. 2026-08-06 22:37 UTCEG score recompute
  49. 2026-08-06 22:07 UTCEG score recompute

Frequently asked(5)

What is CVE-2026-71554?
CVE-2026-71554 is a medium vulnerability published on August 6, 2026. 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…
When was CVE-2026-71554 disclosed?
CVE-2026-71554 was first published in the National Vulnerability Database on August 6, 2026, with the most recent update on September 18, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-71554 actively exploited?
CVE-2026-71554 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 62.1% of all scored CVEs.
What is the CVSS score of CVE-2026-71554?
CVE-2026-71554 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-71554?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-71554, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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