{"api_version":"1","generated_at":"2026-08-29T03:55:32+00:00","cve":"CVE-2026-54556","urls":{"html":"https://cve.report/CVE-2026-54556","api":"https://cve.report/api/cve/CVE-2026-54556.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-54556","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-54556"},"summary":{"title":"Http4s: HTTP/2 Denial of Service with Ember Backend","description":"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.","state":"PUBLISHED","assigner":"GitHub_M","published_at":"2026-08-26 15:16:49","updated_at":"2026-08-29 03:17:07"},"problem_types":["CWE-409","CWE-409 CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)"],"metrics":[{"version":"4.0","source":"security-advisories@github.com","type":"Secondary","score":"8.2","severity":"HIGH","vector":"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","data":{"version":"4.0","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","baseScore":8.2,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}},{"version":"4.0","source":"CNA","type":"DECLARED","score":"8.2","severity":"HIGH","vector":"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","data":{"attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":8.2,"baseSeverity":"HIGH","privilegesRequired":"NONE","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","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","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE"}}],"references":[{"url":"https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e","name":"https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/http4s/http4s/releases/tag/v1.0.0-M47","name":"https://github.com/http4s/http4s/releases/tag/v1.0.0-M47","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm","name":"https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://github.com/http4s/http4s/releases/tag/v0.23.35","name":"https://github.com/http4s/http4s/releases/tag/v0.23.35","refsource":"security-advisories@github.com","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-54556","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-54556","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"http4s","product":"http4s","version":"affected < 0.23.35","platforms":[]},{"source":"CNA","vendor":"http4s","product":"http4s","version":"affected >= 1.0.0-M1, < 1.0.0-M46","platforms":[]},{"source":"CNA","vendor":"org.http4s","product":"http4s-ember-core_2.12","version":"affected < 0.23.35","platforms":[]},{"source":"CNA","vendor":"org.http4s","product":"http4s-ember-core_2.13","version":"affected >= 1.0.0-M1, < 1.0.0-M46","platforms":[]},{"source":"CNA","vendor":"org.http4s","product":"http4s-ember-core_2.13","version":"affected < 0.23.35","platforms":[]},{"source":"CNA","vendor":"org.http4s","product":"http4s-ember-core_3","version":"affected >= 1.0.0-M1, < 1.0.0-M46","platforms":[]},{"source":"CNA","vendor":"org.http4s","product":"http4s-ember-core_3","version":"affected < 0.23.35","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":null,"legacy_qids":[]},"source_records":{"cve_program":{"containers":{"adp":[{"metrics":[{"other":{"content":{"id":"CVE-2026-54556","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","timestamp":"2026-08-29T02:38:20.242464Z","version":"2.0.3"},"type":"ssvc"}}],"providerMetadata":{"dateUpdated":"2026-08-29T02:38:44.725Z","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP"},"title":"CISA ADP Vulnrichment"}],"cna":{"affected":[{"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"}]}],"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."}],"metrics":[{"cvssV4_0":{"attackComplexity":"LOW","attackRequirements":"PRESENT","attackVector":"NETWORK","baseScore":8.2,"baseSeverity":"HIGH","privilegesRequired":"NONE","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","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","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-409","description":"CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)","lang":"en","type":"CWE"}]}],"providerMetadata":{"dateUpdated":"2026-08-26T14:10:22.349Z","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","shortName":"GitHub_M"},"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"}],"source":{"advisory":"GHSA-vmm3-xgcx-67hm","discovery":"UNKNOWN"},"title":"Http4s: HTTP/2 Denial of Service with Ember Backend"}},"cveMetadata":{"assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","assignerShortName":"GitHub_M","cveId":"CVE-2026-54556","datePublished":"2026-08-26T14:10:22.349Z","dateReserved":"2026-06-15T19:04:14.456Z","dateUpdated":"2026-08-29T02:38:44.725Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-08-26 15:16:49","lastModifiedDate":"2026-08-29 03:17:07","problem_types":["CWE-409","CWE-409 CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)"],"metrics":{"cvssMetricV40":[{"source":"security-advisories@github.com","type":"Secondary","cvssData":{"version":"4.0","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","baseScore":8.2,"baseSeverity":"HIGH","attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"PRESENT","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnAvailabilityImpact":"HIGH","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","confidentialityRequirement":"NOT_DEFINED","integrityRequirement":"NOT_DEFINED","availabilityRequirement":"NOT_DEFINED","modifiedAttackVector":"NOT_DEFINED","modifiedAttackComplexity":"NOT_DEFINED","modifiedAttackRequirements":"NOT_DEFINED","modifiedPrivilegesRequired":"NOT_DEFINED","modifiedUserInteraction":"NOT_DEFINED","modifiedVulnConfidentialityImpact":"NOT_DEFINED","modifiedVulnIntegrityImpact":"NOT_DEFINED","modifiedVulnAvailabilityImpact":"NOT_DEFINED","modifiedSubConfidentialityImpact":"NOT_DEFINED","modifiedSubIntegrityImpact":"NOT_DEFINED","modifiedSubAvailabilityImpact":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"NOT_DEFINED"}}],"ssvcV203":[{"source":"134c704f-9b21-4f2e-91b3-4a467353bcc0","ssvcData":{"timestamp":"2026-08-29T02:38:20.242464Z","id":"CVE-2026-54556","options":[{"exploitation":"none"},{"automatable":"yes"},{"technicalImpact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"54556","Ordinal":"1","Title":"Http4s: HTTP/2 Denial of Service with Ember Backend","CVE":"CVE-2026-54556","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"54556","Ordinal":"1","NoteData":"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.","Type":"Description","Title":"Http4s: HTTP/2 Denial of Service with Ember Backend"}]}}}