Http4s Ember HTTP/2: unbounded continuation frame accumulation
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-770.
Summary
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, When Ember receives an HTTP/2 HEADERS or PUSH_PROMISE frame without END_HEADERS, H2Connection buffers the header block and subsequent CONTINUATION fragments without a size bound. A remote peer can keep an incomplete block open and exhaust heap memory before request decoding, affecting an ember-server or ember-client configured with withHttp2. The remediation tracks accumulated size against SETTINGS_MAX_HEADER_LIST_SIZE derived from EmberServerBuilder.maxHeaderSize or EmberClientBuilder.maxResponseHeaderSize, sends GOAWAY when the limit is exceeded, and applies receiveHeadersTimeout to incomplete blocks. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
Why it matters now
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
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| http4s | http4s | before 0.23.35; 1.0.0-M1 to before 1.0.0-M47 | 0.23.35, 1.0.0-M47 | Patch available | CNA |
| — | org.http4s:http4s-ember-core_2.12 (Maven) | before 0.23.35 | 0.23.35 | Patch available | GHSA-cp4q-fqw9-4hf6 |
| — | org.http4s:http4s-ember-core_2.13 (Maven) | before 0.23.35 | 0.23.35 | Patch available | GHSA-cp4q-fqw9-4hf6 |
| — | org.http4s:http4s-ember-core_3 (Maven) | before 0.23.35 | 0.23.35 | Patch available | GHSA-cp4q-fqw9-4hf6 |
| — | org.http4s:http4s-ember-core_2.13 (Maven) | 1.0.0-M1 to before 1.0.0-M47 | 1.0.0-M47 | Patch available | GHSA-cp4q-fqw9-4hf6 |
| — | org.http4s:http4s-ember-core_3 (Maven) | 1.0.0-M1 to before 1.0.0-M47 | 1.0.0-M47 | Patch available | GHSA-cp4q-fqw9-4hf6 |
- http4s Vendorhttp4s Affected before 0.23.35; 1.0.0-M1 to before 1.0.0-M47 Fixed in 0.23.35, 1.0.0-M47 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-cp4q-fqw9-4hf6
- org.http4s:http4s-ember-core_2.13 (Maven) Vendor— Affected before 0.23.35 Fixed in 0.23.35 Patch available GHSA-cp4q-fqw9-4hf6
- org.http4s:http4s-ember-core_3 (Maven) Vendor— Affected before 0.23.35 Fixed in 0.23.35 Patch available GHSA-cp4q-fqw9-4hf6
- 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-cp4q-fqw9-4hf6
- 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-cp4q-fqw9-4hf6
Remediation
- Fix · CNA http4s (http4s) Fixed in 0.23.35, 1.0.0-M47
- Fix · GHSA-cp4q-fqw9-4hf6 org.http4s:http4s-ember-core_2.12 (Maven) Fixed in 0.23.35 Advisory →
- Fix · GHSA-cp4q-fqw9-4hf6 org.http4s:http4s-ember-core_2.13 (Maven) Fixed in 0.23.35 Advisory →
- Fix · GHSA-cp4q-fqw9-4hf6 org.http4s:http4s-ember-core_3 (Maven) Fixed in 0.23.35 Advisory →
- Fix · GHSA-cp4q-fqw9-4hf6 org.http4s:http4s-ember-core_2.13 (Maven) Fixed in 1.0.0-M47 Advisory →
- Fix · GHSA-cp4q-fqw9-4hf6 org.http4s:http4s-ember-core_3 (Maven) Fixed in 1.0.0-M47 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2026-69218
- 2026-10-03 Alias added: GHSA-cp4q-fqw9-4hf6
- 2026-10-28 EPSS moved to the 50th–90th percentile
References
Other 6
- https://github.com/http4s/http4s/security/advisories/GHSA-cp4q-fqw9-4hf6
- https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e
- https://github.com/http4s/http4s/commit/f9dcca4f5a17992ac0972fafd7920f9bc12cdc51
- 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
More http4s vulnerabilities
- 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
Sources
- CVE-2026-69218 · CVE Program
- CVE-2026-69218 · NVD
- FIRST EPSS
- GHSA-cp4q-fqw9-4hf6 · GitHub Advisory Database · CC BY 4.0
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