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GHSA-8f3q-3jmv-7prw

HighCVSS 7.5 / 10
Published Sep 15, 2026·Last modified Sep 15, 2026
Affected Components(5)
Maven logoorg.http4s/http4s-ember-core_3
< 0.23.35
Maven logoorg.http4s/http4s-ember-core_2.13
< 0.23.35
Maven logoorg.http4s/http4s-ember-core_3
1.0.0-M1 – 1.0.0-M47
1 / 2
Description

Ember's HTTP/2 connection serializes all outgoing frames through a single unbounded queue drained by one writer fiber (writeLoop). When the write side stalls, any frames the connection keeps producing accumulate in that queue without limit. The peer can drive this cheaply because the connection emits a control frame in response to inbound frames it does not flow-control: one PING ACK per PING, one SETTINGS ACK per SETTINGS, and a WINDOW_UPDATE per inbound DATA. A single unauthenticated connection can therefore exhaust heap and OOM the process.

This affects an ember server (malicious client) and an ember client (malicious/compromised server that floods the client and stops reading its ACKs).

Impact

Unauthenticated remote denial of service (OOM) against any ember server built .withHttp2, from a single connection, at negligible attacker cost (tiny control frames). Also affects an ember client talking to a hostile HTTP/2 server.

Preconditions

  • Ember server or client built .withHttp2, speaking to a hostile or compromised peer.

Workarounds

  • Disable HTTP/2 (do not call .withHttp2).
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Risk Scores
Base Score
7.5

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the availability of the system.

Threat Intelligence
6.9

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
0.63%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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