CVE-2026-54556

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.

CVSS

No CVSS.

References

Link	Resource
https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e
https://github.com/http4s/http4s/releases/tag/v0.23.35
https://github.com/http4s/http4s/releases/tag/v1.0.0-M47
https://github.com/http4s/http4s/security/advisories/GHSA-vmm3-xgcx-67hm

Configurations

No configuration.

History

No history.

Information

Published : 2026-08-26 15:16

Updated : 2026-09-09 21:09

NVD link : CVE-2026-54556

Mitre link : CVE-2026-54556

CVE.ORG link : CVE-2026-54556

JSON object : View

Products Affected

No product.

CWE

CWE-409

Improper Handling of Highly Compressed Data (Data Amplification)

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