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GHSA-9vwc-pc8p-253q

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

An ember server with HTTP/2 enabled (.withHttp2) does not enforce SETTINGS_MAX_CONCURRENT_STREAMS on streams opened by the peer. A single unauthenticated connection can open an unbounded number of concurrent streams, each of which allocates per-stream server state that is never released, exhausting the heap.

Impact

Unauthenticated remote denial of service (memory exhaustion) against any Ember server built .withHttp2. This is the resource-exhaustion class of the HTTP/2 "Rapid Reset" family (CVE-2023-44487).

The same unchecked allocation path is reachable on the client via server-initiated PUSH_PROMISE frames, so a malicious or compromised server can exhaust an ember-client's heap the same way.

Preconditions

  • Server: with .withHttp2 enabled.
  • Client: makes HTTP/2 requests to malicious or compromised sites. enablePush is not enforced.

Workarounds

  • Disable HTTP/2 on EmberServerBuilder or EmberClientBuilder (default)
  • Client only: avoid HTTP/2 to untrusted servers until patched.
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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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