CVE-2026-54556 (GCVE-0-2026-54556)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:10 – Updated: 2026-08-26 14:10
VLAI
Title
Http4s: HTTP/2 Denial of Service with Ember Backend
Summary
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, an unauthenticated HTTP/2 peer can cause an out-of-memory denial of service in the Ember backend with HTTP/2 enabled. The Hpack wrapper in ember-core/shared/src/main/scala/org/http4s/ember/core/h2/Hpack.scala concatenates HEADERS and CONTINUATION frame fragments and decodes them into a single List, but maxHeaderSize accounting does not include indexed headers or HPACK per-header overhead. A small compressed header block can therefore expand into a much larger decoded representation that remains in memory for processing. Servers exposed to untrusted HTTP/2 traffic and clients directed to an untrusted HTTP/2 server are affected, and concurrent malicious connections can exhaust the process heap. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Severity
8.2 (High)
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CWE
  • CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)
Assigner
References
Impacted products
Vendor Product Version CPE status
http4s http4s Affected: < 0.23.35
Affected: >= 1.0.0-M1, < 1.0.0-M46
guessed Create a notification for this product.
org.http4s http4s-ember-core_2.12 Affected: < 0.23.35
guessed Create a notification for this product.
org.http4s http4s-ember-core_2.13 Affected: >= 1.0.0-M1, < 1.0.0-M46
Affected: < 0.23.35
guessed Create a notification for this product.
org.http4s http4s-ember-core_3 Affected: >= 1.0.0-M1, < 1.0.0-M46
Affected: < 0.23.35
guessed Create a notification for this product.
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{
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        },
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              "version": "\u003c 0.23.35"
            }
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        }
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            "subConfidentialityImpact": "NONE",
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            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
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              "type": "CWE"
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      "providerMetadata": {
        "dateUpdated": "2026-08-26T14:10:22.349Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
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          "name": "https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm",
          "tags": [
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        {
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        },
        {
          "name": "https://github.com/http4s/http4s/releases/tag/v0.23.35",
          "tags": [
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          ],
          "url": "https://github.com/http4s/http4s/releases/tag/v0.23.35"
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          "name": "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47",
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          "url": "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47"
        }
      ],
      "source": {
        "advisory": "GHSA-vmm3-xgcx-67hm",
        "discovery": "UNKNOWN"
      },
      "title": "Http4s: HTTP/2 Denial of Service with Ember Backend"
    }
  },
  "cveMetadata": {
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    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-54556",
    "datePublished": "2026-08-26T14:10:22.349Z",
    "dateReserved": "2026-06-15T19:04:14.456Z",
    "dateUpdated": "2026-08-26T14:10:22.349Z",
    "state": "PUBLISHED"
  },
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      "date": "2026-08-28",
      "epss": "0.00302",
      "percentile": "0.22265"
    },
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  }
}



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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


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