AIKIDO-2026-254483

http4s-ember-core_2.12 is vulnerable to Denial of Service (DoS)

GHSA-3q2f-8v8m-249pPublished Sep 23, 2026

CVE Score

High

Denial of Service (DoS)

TL;DR

Ember HTTP/2 handling only checks a buffered CONTINUATION header block against maxHeaderBlockSize while endHeaders is false, and it never checks CONTINUATION payloads against maxFrameSize. The frame that sets endHeaders=true finishes the header block with no size check. A peer can send a small HEADERS frame with endHeaders=false plus one CONTINUATION frame with endHeaders=true and a payload of about 16MB, which bypasses the header block size limit and makes the server buffer that payload before HPACK decoding fails, so repeating this across streams exhausts server memory. The fix applies the same maxHeaderBlockSize check to the terminating CONTINUATION frame.

How do I fix this?

Upgrade the http4s-ember-core_2.12 library to the patch version.

Who does this affect?

You are affected if you are using a version that falls within the vulnerable range and you accept HTTP/2 connections through Ember over TLS+ALPN or cleartext prior knowledge.