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GHSA-6m4x-pp6q-5jmm

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 stack replenishes the inbound flow-control window based on bytes received off the wire, not bytes consumed by the application. Received DATA is buffered in an unbounded per-stream channel. Flow control therefore provides no backpressure: a peer can stream a large or unbounded body faster than the application drains it and the connection retains every payload in heap.

This is the read-path mirror of the outbound queue issue.

This affects an Ember receiving a request body and an Ember client receiving a response body from a hostile server.

Impact

Unauthenticated remote denial of service (OOM) against any Ember server built .withHttp2 for a non-draining or slow-draining route, and against an Ember client consuming from a hostile or compromised server.

Workarounds

  • Disable HTTP/2 to remove the vector entirely.
  • Apply an aggregate request-entity size limit (e.g. EntityLimiter middleware) on routes that consume the body.
  • Ensure handlers fully drain request bodies with aggressive idle timeouts.
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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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