{
    "dataType": "CVE_RECORD",
    "dataVersion": "5.2",
    "cveMetadata": {
        "cveId": "CVE-2026-54556",
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "state": "PUBLISHED",
        "assignerShortName": "GitHub_M",
        "dateReserved": "2026-06-15T19:04:14.456Z",
        "datePublished": "2026-08-26T14:10:22.349Z",
        "dateUpdated": "2026-08-26T14:10:22.349Z"
    },
    "containers": {
        "cna": {
            "title": "Http4s: HTTP/2 Denial of Service with Ember Backend",
            "problemTypes": [
                {
                    "descriptions": [
                        {
                            "cweId": "CWE-409",
                            "lang": "en",
                            "description": "CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)",
                            "type": "CWE"
                        }
                    ]
                }
            ],
            "metrics": [
                {
                    "cvssV4_0": {
                        "attackVector": "NETWORK",
                        "attackComplexity": "LOW",
                        "attackRequirements": "PRESENT",
                        "privilegesRequired": "NONE",
                        "userInteraction": "NONE",
                        "vulnConfidentialityImpact": "NONE",
                        "vulnIntegrityImpact": "NONE",
                        "vulnAvailabilityImpact": "HIGH",
                        "subConfidentialityImpact": "NONE",
                        "subIntegrityImpact": "NONE",
                        "subAvailabilityImpact": "NONE",
                        "baseScore": 8.2,
                        "baseSeverity": "HIGH",
                        "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",
                        "version": "4.0"
                    }
                }
            ],
            "references": [
                {
                    "name": "https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm",
                    "tags": [
                        "x_refsource_CONFIRM"
                    ],
                    "url": "https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm"
                },
                {
                    "name": "https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e",
                    "tags": [
                        "x_refsource_MISC"
                    ],
                    "url": "https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e"
                },
                {
                    "name": "https://github.com/http4s/http4s/releases/tag/v0.23.35",
                    "tags": [
                        "x_refsource_MISC"
                    ],
                    "url": "https://github.com/http4s/http4s/releases/tag/v0.23.35"
                },
                {
                    "name": "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47",
                    "tags": [
                        "x_refsource_MISC"
                    ],
                    "url": "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47"
                }
            ],
            "affected": [
                {
                    "vendor": "http4s",
                    "product": "http4s",
                    "versions": [
                        {
                            "version": "< 0.23.35",
                            "status": "affected"
                        },
                        {
                            "version": ">= 1.0.0-M1, < 1.0.0-M46",
                            "status": "affected"
                        }
                    ]
                },
                {
                    "vendor": "org.http4s",
                    "product": "http4s-ember-core_2.12",
                    "versions": [
                        {
                            "version": "< 0.23.35",
                            "status": "affected"
                        }
                    ]
                },
                {
                    "vendor": "org.http4s",
                    "product": "http4s-ember-core_2.13",
                    "versions": [
                        {
                            "version": ">= 1.0.0-M1, < 1.0.0-M46",
                            "status": "affected"
                        },
                        {
                            "version": "< 0.23.35",
                            "status": "affected"
                        }
                    ]
                },
                {
                    "vendor": "org.http4s",
                    "product": "http4s-ember-core_3",
                    "versions": [
                        {
                            "version": ">= 1.0.0-M1, < 1.0.0-M46",
                            "status": "affected"
                        },
                        {
                            "version": "< 0.23.35",
                            "status": "affected"
                        }
                    ]
                }
            ],
            "providerMetadata": {
                "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
                "shortName": "GitHub_M",
                "dateUpdated": "2026-08-26T14:10:22.349Z"
            },
            "descriptions": [
                {
                    "lang": "en",
                    "value": "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."
                }
            ],
            "source": {
                "advisory": "GHSA-vmm3-xgcx-67hm",
                "discovery": "UNKNOWN"
            }
        }
    }
}