High severity · published Sep 15, 2026
CVE-2026-69218
Http4s Ember HTTP/2: unbounded continuation frame accumulation
7.5
CVSS
0.6%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.6% · higher than 50% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
HT
http4s · http4s
< 0.23.35; >= 1.0.0-M1, < 1.0.0-M47 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-69218
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-69218
github.com
https://github.com/http4s/http4s/commit/6e8eccd64a6a74ab4811897881e95e0e1b3a818e
github.com
https://github.com/http4s/http4s/commit/f9dcca4f5a17992ac0972fafd7920f9bc12cdc51
github.com
https://github.com/http4s/http4s/releases/tag/v0.23.35
github.com
https://github.com/http4s/http4s/releases/tag/v1.0.0-M47
github.com
https://github.com/http4s/http4s/security/advisories/GHSA-cp4q-fqw9-4hf6
More from http4s
9.2
CVE-2026-69204
Http4s: Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)
8.7
CVE-2026-69217
Http4s: Ember Server accepts duplicate Content-Length headers
8.7
CVE-2026-69205
Http4s: Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)
8.2
CVE-2026-54556
Http4s: HTTP/2 Denial of Service with Ember Backend
7.5
CVE-2026-88975
Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE