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TI-2026-39394 Aliases CVE-2026-54556GHSA-vmm3-xgcx-67hm

Http4s: HTTP/2 Denial of Service with Ember Backend

Priority MEDIUM 42CWE-409Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00524 44th percentileScored 2026-11-07
Fix Fixed http4s (http4s): 0.23.35, 1.0.0-M46http4s-ember-core_2.12 (org.http4s): 0.23.35+5 more products

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
http4shttp4sbefore 0.23.35; 1.0.0-M1 to before 1.0.0-M460.23.35, 1.0.0-M46Patch availableCNA
org.http4shttp4s-ember-core_2.12before 0.23.350.23.35Patch availableCNA
org.http4shttp4s-ember-core_2.131.0.0-M1 to before 1.0.0-M46; before 0.23.351.0.0-M46, 0.23.35Patch availableCNA
org.http4shttp4s-ember-core_31.0.0-M1 to before 1.0.0-M46; before 0.23.351.0.0-M46, 0.23.35Patch availableCNA
—org.http4s:http4s-ember-core_2.12 (Maven)before 0.23.350.23.35Patch availableGHSA-vmm3-xgcx-67hm
—org.http4s:http4s-ember-core_2.13 (Maven)1.0.0-M1 to before 1.0.0-M471.0.0-M47Patch availableGHSA-vmm3-xgcx-67hm
—org.http4s:http4s-ember-core_3 (Maven)before 0.23.350.23.35Patch availableGHSA-vmm3-xgcx-67hm
—org.http4s:http4s-ember-core_3 (Maven)1.0.0-M1 to before 1.0.0-M471.0.0-M47Patch availableGHSA-vmm3-xgcx-67hm
—org.http4s:http4s-ember-core_2.13 (Maven)before 0.23.350.23.35Patch availableGHSA-vmm3-xgcx-67hm
  • http4s Vendorhttp4s Affected before 0.23.35; 1.0.0-M1 to before 1.0.0-M46 Fixed in 0.23.35, 1.0.0-M46 Patch available CNA
  • http4s-ember-core_2.12 Vendororg.http4s Affected before 0.23.35 Fixed in 0.23.35 Patch available CNA
  • http4s-ember-core_2.13 Vendororg.http4s Affected 1.0.0-M1 to before 1.0.0-M46; before 0.23.35 Fixed in 1.0.0-M46, 0.23.35 Patch available CNA
  • http4s-ember-core_3 Vendororg.http4s Affected 1.0.0-M1 to before 1.0.0-M46; before 0.23.35 Fixed in 1.0.0-M46, 0.23.35 Patch available CNA
  • org.http4s:http4s-ember-core_2.12 (Maven) Vendor— Affected before 0.23.35 Fixed in 0.23.35 Patch available GHSA-vmm3-xgcx-67hm
  • org.http4s:http4s-ember-core_2.13 (Maven) Vendor— Affected 1.0.0-M1 to before 1.0.0-M47 Fixed in 1.0.0-M47 Patch available GHSA-vmm3-xgcx-67hm
  • org.http4s:http4s-ember-core_3 (Maven) Vendor— Affected before 0.23.35 Fixed in 0.23.35 Patch available GHSA-vmm3-xgcx-67hm
  • org.http4s:http4s-ember-core_3 (Maven) Vendor— Affected 1.0.0-M1 to before 1.0.0-M47 Fixed in 1.0.0-M47 Patch available GHSA-vmm3-xgcx-67hm
  • org.http4s:http4s-ember-core_2.13 (Maven) Vendor— Affected before 0.23.35 Fixed in 0.23.35 Patch available GHSA-vmm3-xgcx-67hm

CPE names Threatist (inferred) · 1

Inferred from how NVD named this product before; not given by a source.

CPEVersionsRoleVendor
cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:*——http4s
  • cpe:2.3:a:typelevel:http4s:*:*:*:*:*:*:*:* Versions — — ·http4s

Remediation

  • Fix · CNA http4s (http4s) Fixed in 0.23.35, 1.0.0-M46
  • Fix · CNA http4s-ember-core_2.12 (org.http4s) Fixed in 0.23.35
  • Fix · CNA http4s-ember-core_2.13 (org.http4s) Fixed in 1.0.0-M46, 0.23.35
  • Fix · CNA http4s-ember-core_3 (org.http4s) Fixed in 1.0.0-M46, 0.23.35
  • Fix · GHSA-vmm3-xgcx-67hm org.http4s:http4s-ember-core_2.12 (Maven) Fixed in 0.23.35 Advisory →
  • Fix · GHSA-vmm3-xgcx-67hm org.http4s:http4s-ember-core_2.13 (Maven) Fixed in 1.0.0-M47 Advisory →
  • Fix · GHSA-vmm3-xgcx-67hm org.http4s:http4s-ember-core_3 (Maven) Fixed in 0.23.35 Advisory →
  • Fix · GHSA-vmm3-xgcx-67hm org.http4s:http4s-ember-core_3 (Maven) Fixed in 1.0.0-M47 Advisory →
  • Fix · GHSA-vmm3-xgcx-67hm org.http4s:http4s-ember-core_2.13 (Maven) Fixed in 0.23.35 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-54556
  2. 2026-10-03 Alias added: GHSA-vmm3-xgcx-67hm

References

Other 5

  • TI-2022-13223 mTLS client verification is skipped in fs2 on Node.js CVSS 3.1CRITICAL 9.8
  • TI-2023-08714 Http4s has fatal error parsing User-Agent and Server headers CVSS 3.1HIGH 7.5
  • TI-2022-06031 Hash collision in typelevel jawn CVSS 3.1HIGH 7.5
  • TI-2025-37261 Http4s vulnerable to HTTP Request Smuggling due to improper handling of HTTP trailer section CVSS 4.0MEDIUM 6.3
  • TI-2026-44185 http4s-scala-xml has an XML External Entity (XXE) processing issue CVSS 3.1CRITICAL 9.3
  • TI-2020-04336 Local file inclusion vulnerability in http4s CVSS 3.1HIGH 7.6
See all 36 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences