{"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"}}}}

{}

{"affected": [{"affectedData": [{"product": "http4s", "vendor": "http4s", "versions": [{"status": "affected", "version": "< 0.23.35"}, {"status": "affected", "version": ">= 1.0.0-M1, < 1.0.0-M46"}]}, {"product": "http4s-ember-core_2.12", "vendor": "org.http4s", "versions": [{"status": "affected", "version": "< 0.23.35"}]}, {"product": "http4s-ember-core_2.13", "vendor": "org.http4s", "versions": [{"status": "affected", "version": ">= 1.0.0-M1, < 1.0.0-M46"}, {"status": "affected", "version": "< 0.23.35"}]}, {"product": "http4s-ember-core_3", "vendor": "org.http4s", "versions": [{"status": "affected", "version": ">= 1.0.0-M1, < 1.0.0-M46"}, {"status": "affected", "version": "< 0.23.35"}]}], "source": "security-advisories@github.com"}], "cveTags": [], "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."}], "id": "CVE-2026-54556", "lastModified": "2026-08-26T15:16:49.527", "metrics": {"cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "PRESENT", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 8.2, "baseSeverity": "HIGH", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X", "version": "4.0", "vulnAvailabilityImpact": "HIGH", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "security-advisories@github.com", "type": "Secondary"}]}, "published": "2026-08-26T15:16:49.527", "references": [{"source": "security-advisories@github.com", "url": "https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e"}, {"source": "security-advisories@github.com", "url": "https://github.com/http4s/http4s/releases/tag/v0.23.35"}, {"source": "security-advisories@github.com", "url": "https://github.com/http4s/http4s/releases/tag/v1.0.0-M47"}, {"source": "security-advisories@github.com", "url": "https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm"}], "sourceIdentifier": "security-advisories@github.com", "vulnStatus": "Received", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-409"}], "source": "security-advisories@github.com", "type": "Primary"}]}

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