CVE-2026-69213High· 7.5▾ TwilightHttp4s 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 c…
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0.1 · exploitation 0
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Stakeholder-Specific Vulnerability Categorization from CISA's ADP record at CVE.org: whether exploitation is observed, whether an attack can be automated, and how much of the system is at stake.
Exploit-prediction probability, daily snapshots since Sep 17.
Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via NVD
Last analysed / modified upstream
0.4%
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.
Refer to the linked advisories for vendor-supplied fixes and affected version ranges.
Affected packages:
org.http4s:http4s-ember-core_2.12 <= 0.23.34org.http4s:http4s-ember-core_2.13 <= 0.23.34org.http4s:http4s-ember-core_3 <= 0.23.34org.http4s:http4s-ember-core_3 >= 1.0.0-M1, <= 1.0.0-M46org.http4s:http4s-ember-core_2.13 >= 1.0.0-M1, <= 1.0.0-M46Patched in:
org.http4s:http4s-ember-core_2.12 0.23.35org.http4s:http4s-ember-core_2.13 0.23.35org.http4s:http4s-ember-core_3 0.23.35org.http4s:http4s-ember-core_3 1.0.0-M47org.http4s:http4s-ember-core_2.13 1.0.0-M47Connected by shared product, vendor, weakness, or advisory.
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