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    CVE-2026-54340

    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.

    Published:Jul 16, 2026
    Last Modified:Jul 17, 2026
    EPS:Jul 16, 2026
    EPSS Score:0.00278
    CVSS Score:7.5

    Affected Products

    Vendor
    H2o
    Product
    H2o

    Exploits

    No exploit reference

    Related CVEs

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    CVE-2026-8751 (CVSS 5.5) — A security flaw has been discovered in h2oai h2o-3 up to 7402. This affects the function importBinaryModel of …
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    CVE-2025-10769 (CVSS 2.1) — A vulnerability has been found in h2oai h2o-3 up to 3.46.08. This affects an unknown function of the file /99/…
    CVE-2025-10768 (CVSS 2.1) — A flaw has been found in h2oai h2o-3 up to 3.46.08. The impacted element is an unknown function of the file /9…
    CVE-2025-6544 (CVSS 9.8) — A deserialization vulnerability exists in h2oai/h2o-3 versions <= 3.46.0.8, allowing attackers to read arbitra…

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High