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

Vulnerability from nvd – Published: 2026-08-26 14:10 – Updated: 2026-08-26 14:10

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

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/http4s/http4s/security/advisor…	x_refsource_CONFIRM
https://github.com/http4s/http4s/commit/6e8eccd64…	x_refsource_MISC
https://github.com/http4s/http4s/releases/tag/v0.23.35	x_refsource_MISC
https://github.com/http4s/http4s/releases/tag/v1.…	x_refsource_MISC

Impacted products

4 products

Vendor	Product	Version
http4s	http4s	Affected: < 0.23.35 Affected: >= 1.0.0-M1, < 1.0.0-M46
org.http4s	http4s-ember-core_2.12	Affected: < 0.23.35
org.http4s	http4s-ember-core_2.13	Affected: >= 1.0.0-M1, < 1.0.0-M46 Affected: < 0.23.35
org.http4s	http4s-ember-core_3	Affected: >= 1.0.0-M1, < 1.0.0-M46 Affected: < 0.23.35

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "http4s",
          "vendor": "http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            }
          ]
        },
        {
          "product": "http4s-ember-core_2.12",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            }
          ]
        },
        {
          "product": "http4s-ember-core_2.13",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            },
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            }
          ]
        },
        {
          "product": "http4s-ember-core_3",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            },
            {
              "status": "affected",
              "version": "\u003c 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": "2026-08-26T14:10:22.349Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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

Vulnerability from cvelistv5 – Published: 2026-08-26 14:10 – Updated: 2026-08-26 14:10

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

GitHub_M mitre root

References

4 references

URL	Tags
https://github.com/http4s/http4s/security/advisor…	x_refsource_CONFIRM
https://github.com/http4s/http4s/commit/6e8eccd64…	x_refsource_MISC
https://github.com/http4s/http4s/releases/tag/v0.23.35	x_refsource_MISC
https://github.com/http4s/http4s/releases/tag/v1.…	x_refsource_MISC

Impacted products

4 products

Vendor	Product	Version
http4s	http4s	Affected: < 0.23.35 Affected: >= 1.0.0-M1, < 1.0.0-M46
org.http4s	http4s-ember-core_2.12	Affected: < 0.23.35
org.http4s	http4s-ember-core_2.13	Affected: >= 1.0.0-M1, < 1.0.0-M46 Affected: < 0.23.35
org.http4s	http4s-ember-core_3	Affected: >= 1.0.0-M1, < 1.0.0-M46 Affected: < 0.23.35

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "http4s",
          "vendor": "http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            },
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            }
          ]
        },
        {
          "product": "http4s-ember-core_2.12",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            }
          ]
        },
        {
          "product": "http4s-ember-core_2.13",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            },
            {
              "status": "affected",
              "version": "\u003c 0.23.35"
            }
          ]
        },
        {
          "product": "http4s-ember-core_3",
          "vendor": "org.http4s",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 1.0.0-M1, \u003c 1.0.0-M46"
            },
            {
              "status": "affected",
              "version": "\u003c 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": "2026-08-26T14:10:22.349Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Find a vulnerability

Search criteria ⓘ Use this form to refine search results.
Full-text search supports keyword queries with ranking and filtering.
You can combine vendor, product, and sources to narrow results.
Enable “Apply ordering” to sort by date instead of relevance.

2 vulnerabilities by org.http4s

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

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

Find a vulnerability

Search criteria ⓘ Use this form to refine search results. Full-text search supports keyword queries with ranking and filtering. You can combine vendor, product, and sources to narrow results. Enable “Apply ordering” to sort by date instead of relevance.

2 vulnerabilities by org.http4s

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

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

Search criteria ⓘ Use this form to refine search results.
Full-text search supports keyword queries with ranking and filtering.
You can combine vendor, product, and sources to narrow results.
Enable “Apply ordering” to sort by date instead of relevance.