H2O HPACK Decompressor state issue

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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5.1$0-$5k1.40+

Summaryinfo

A vulnerability categorized as problematic has been discovered in H2O. Affected by this issue is some unknown functionality of the component HPACK Decompressor. Such manipulation leads to state issue. This vulnerability is listed as CVE-2026-54340. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in H2O (affected version unknown) and classified as problematic. Affected by this issue is an unknown functionality of the component HPACK Decompressor. The manipulation with an unknown input leads to a state issue vulnerability. Using CWE to declare the problem leads to CWE-371. Impacted is availability. CVE summarizes:

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd.

The advisory is shared for download at github.com. This vulnerability is handled as CVE-2026-54340 since 06/12/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are neither technical details nor an exploit publicly available.

Applying the patch 9265bdd is able to eliminate this problem.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Name

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 5.3
VulDB Meta Temp Score: 5.1

VulDB Base Score: 5.3
VulDB Temp Score: 5.1
VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: State issue
CWE: CWE-371
CAPEC: 🔒
ATT&CK: 🔒

Physical: No
Local: No
Remote: Yes

Availability: 🔒
Status: Not defined
Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: no mitigation known
Status: 🔍

0-Day Time: 🔒

Patch: 9265bdd

Timelineinfo

06/12/2026 CVE reserved
07/17/2026 +35 days Advisory disclosed
07/17/2026 +0 days VulDB entry created
07/17/2026 +0 days VulDB entry last update

Sourcesinfo

Product: github.com

Advisory: github.com
Status: Confirmed

CVE: CVE-2026-54340 (🔒)
GCVE (CVE): GCVE-0-2026-54340
GCVE (VulDB): GCVE-100-379688

Entryinfo

Created: 07/17/2026 02:09
Changes: 07/17/2026 02:09 (51)
Complete: 🔍
Cache ID: 216::103

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