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CVE-2026-23527

H3 vulnerability

8.9 HIGHPublic exploitEPSS 0.64%
  1. Published15 Jan 2026

Description

H3 is a minimal H(TTP) framework built for high performance and portability. Prior to 1.15.5, there is a critical HTTP Request Smuggling vulnerability. readRawBody is doing a strict case-sensitive check for the Transfer-Encoding header. It explicitly looks for "chunked", but per the RFC, this header should be case-insensitive. This vulnerability is fixed in 1.15.5.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityHigh
Privileges requiredNone
User interactionNone
ScopeChanged
ConfidentialityHigh
IntegrityHigh
AvailabilityLow
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:L

Affected products

H3< 1.15.5

Remediation

Fixed in
H3≥ 1.15.5

References

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Frequently asked

Is CVE-2026-23527 being actively exploited?

CVE-2026-23527 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.64%.

How severe is CVE-2026-23527?

CVE-2026-23527 has a CVSS 3.1 base score of 8.9, rated high. EPSS estimates a 0.64% probability of exploitation.

Which products are affected by CVE-2026-23527?

Affected products include H3.

How do I fix CVE-2026-23527?

Upgrade affected software to a fixed version, for example H3 1.15.5 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.