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GHSA-cqgj-h8vf-4w59

HighCVSS 7.5 / 10
Published Jun 10, 2026·Last modified Jun 10, 2026
Affected Components(0)

No affected components available

Description

Impact

Bad clients that always send a fixed batch value while the server is using the acknowledgement extension can cause the unacknowledged message queue to grow indefinitely, eventually resulting in an OutOfMemoryError.

Such bad clients would always send:

{
  "channel": "/meta/connect",
  ...
  "ext": { "ack": 1 }
}

The server would never clear the unacknowledged message queue, and one bad client can cause a server outage.

Patches

5.0.x - https://github.com/cometd/cometd/pull/2168 6.0.x - https://github.com/cometd/cometd/pull/2169 8.0.x - https://github.com/cometd/cometd/pull/2118

Workarounds

Disable the acknowledgement extension.

Resources

https://github.com/cometd/cometd/discussions/2116 https://github.com/cometd/cometd/issues/2117

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
0.68%

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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