CVSS 4.0
8.2 highCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NCVE-2026-54556
High (8.2). EPSS 0.5% chance of exploitation in the next 30 days. Fixed in org.http4s:http4s-ember-core_2.12 0.23.35.
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
- EPSS
- 0.5% chance of exploitation in the next 30 days; higher than 44% of CVEs (scores of 2026-10-31)
- CWE
- CWE-409
- Published
- Modified
- Record from
- the NVD, synced
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-vmm3-xgcx-67hm | Maven | org.http4s:http4s-ember-core_2.12 | <0.23.35 | 0.23.35 |
| GHSA-vmm3-xgcx-67hm | Maven | org.http4s:http4s-ember-core_2.13 | >=1.0.0-M1 <1.0.0-M47 | 1.0.0-M47 |
| GHSA-vmm3-xgcx-67hm | Maven | org.http4s:http4s-ember-core_3 | <0.23.35 | 0.23.35 |
| GHSA-vmm3-xgcx-67hm | Maven | org.http4s:http4s-ember-core_3 | >=1.0.0-M1 <1.0.0-M47 | 1.0.0-M47 |
| GHSA-vmm3-xgcx-67hm | Maven | org.http4s:http4s-ember-core_2.13 | <0.23.35 | 0.23.35 |