Improper Handling of Highly Compressed Data (Data Amplification) Affecting org.http4s:http4s-ember-core_2.12 package, versions [,0.23.35)
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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- published27 Aug 2026
- disclosed26 Aug 2026
- creditreardonj
Introduced: 26 Aug 2026
NewCVE-2026-54556 (opens in a new tab)How to fix?
Upgrade org.http4s:http4s-ember-core_2.12 to version 0.23.35 or higher.
Overview
Affected versions of this package are vulnerable to Improper Handling of Highly Compressed Data (Data Amplification) through the Hpack.decodeHeaders path in ember-core/shared/src/main/scala/org/http4s/ember/core/h2/Hpack.scala. An attacker can exhaust heap memory and crash an HTTP/2 server or client by sending HPACK-encoded header blocks that expand into a large decoded header list, bypassing the header-size accounting used by Ember’s HTTP/2 header processing. The vulnerable decoder concatenates and materializes the full header list before enforcing a meaningful limit, so small input packets can expand into a much larger in-memory result. On exposed Ember HTTP/2 deployments, repeated malicious requests can trigger OutOfMemoryError and stop request handling for legitimate traffic.
Workarounds
- Disable HTTP/2 in Ember backends to prevent exposure to the HPACK bomb attack path.