How severe is CVE-2026-23527?

CVE-2026-23527 has a CVSS 3.x base score of 8.9, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability low.

Is CVE-2026-23527 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-23527?

CVE-2026-23527 affects H3. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-23527?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-23527 have an EU (EUVD) identifier?

Yes. CVE-2026-23527 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-2737.

When was CVE-2026-23527 published?

CVE-2026-23527 was published on 2026-01-15 and last updated on 2026-06-17.

CVE-2026-23527

CVE-2026-23527 is a high-severity vulnerability in H3 with a CVSS 3.x base score of 8.9. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-444.

Key facts

Severity: High (CVSS 3.x base score 8.9)
EPSS exploit prediction: 1% (43rd percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-2737
Weakness: CWE-444
Affected product: H3
Published: 2026-01-15
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2026-23527?: 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.
How severe is CVE-2026-23527?: CVE-2026-23527 has a CVSS 3.x base score of 8.9, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability low.
Is CVE-2026-23527 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (43rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-23527?: CVE-2026-23527 affects H3. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-23527?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-23527 have an EU (EUVD) identifier?: Yes. CVE-2026-23527 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-2737.
When was CVE-2026-23527 published?: CVE-2026-23527 was published on 2026-01-15 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:h3:h3:*:*:*:*:*:node.js:*:*

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