High severity · published Sep 15, 2026
CVE-2026-69213
Http4s Ember HTTP/2: unbounded outbound frame queue
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, Ember HTTP/2 serializes outbound frames through one unbounded queue consumed by writeLoop. When the peer stops reading, an unauthenticated HTTP/2 client can continue sending PING, SETTINGS, or DATA frames that cause Ember to enqueue acknowledgments or WINDOW_UPDATE frames faster than the writer drains them, exhausting heap memory on a server built with withHttp2. The shared behavior also affects an ember-client connected to a hostile HTTP/2 server, and the patch replaces the unbounded path with bounded, backpressured outbound queues. 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-2026-69213
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-69213
github.com
https://github.com/http4s/http4s/commit/13fe24d6440bde2f1eb70121486cf59c278e6bae
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-8f3q-3jmv-7prw
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