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Acknowledgement extension out of memory

High severity GitHub Reviewed Published Jun 10, 2026 in cometd/cometd • Updated Jun 10, 2026

Package

maven org.cometd.java:cometd-java-server-common (Maven)

Affected versions

>= 5.0.0, <= 5.0.22
>= 6.0.0, <= 6.0.18
>= 7.0.0, <= 7.0.18
>= 8.0.0, <= 8.0.8

Patched versions

5.0.23
6.0.19
7.0.19
8.0.9

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 - cometd/cometd#2168
6.0.x - cometd/cometd#2169
8.0.x - cometd/cometd#2118

Workarounds

Disable the acknowledgement extension.

Resources

cometd/cometd#2116
cometd/cometd#2117

References

@sbordet sbordet published to cometd/cometd Jun 10, 2026
Published to the GitHub Advisory Database Jun 10, 2026
Reviewed Jun 10, 2026
Last updated Jun 10, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(49th percentile)

Weaknesses

Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource. Learn more on MITRE.

CVE ID

CVE-2025-53114

GHSA ID

GHSA-cqgj-h8vf-4w59

Source code

Credits

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