{"apiVersion":"1.0","identifier":"CVE-2026-54556","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.","publishedAt":"2026-08-26T15:16:49","lastModifiedAt":"2026-08-26T15:16:49","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-54556","cvssScore":8.2,"cvssVector":"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","epssProbability":0.00302,"riskScore":0.84,"affectedProduct":"Http4s","affectedVersions":"cannotmatch","vulnerabilityType":"Library","operatingSystems":[],"links":{"self":"https://www.redsauce.net/api/cves/CVE-2026-54556","webPages":{"es":"https://www.redsauce.net/es/cves/CVE-2026-54556","en":"https://www.redsauce.net/en/cves/CVE-2026-54556","fr":"https://www.redsauce.net/fr/cves/CVE-2026-54556","pt":"https://www.redsauce.net/pt/cves/CVE-2026-54556","de":"https://www.redsauce.net/de/cves/CVE-2026-54556","sk":"https://www.redsauce.net/sk/cves/CVE-2026-54556","el":"https://www.redsauce.net/el/cves/CVE-2026-54556"},"source":"https://nvd.nist.gov/vuln/detail/CVE-2026-54556"}}