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GHSA-qrvq-68c2-7grw

MediumCVSS 5.9 / 10
Published Feb 24, 2026·Last modified Apr 2, 2026
Affected Components(0)

No affected components available

Description

Impact

The WebSockets handling of NATS messages handles compressed messages via the WebSockets negotiated compression. The implementation bound the memory size of a NATS message but did not independently bound the memory consumption of the memory stream when constructing a NATS message which might then fail validation for size reasons.

An attacker can use a compression bomb to cause excessive memory consumption, often resulting in the operating system terminating the server process.

The use of compression is negotiated before authentication, so this does not require valid NATS credentials to exploit.

The fix was to bounds the decompression to fail once the message was too large, instead of continuing on.

Patches

This was released in nats-server without being highlighted as a security issue. It should have been, this was an oversight. Per the NATS security policy, because this does not require a valid user, it is CVE-worthy.

This was fixed in the v2.11 series with v2.11.12 and in the v2.12 series with v2.12.3.

Workarounds

This only affects deployments which use WebSockets and which expose the network port to untrusted end-points.

References

This was reported to the NATS maintainers by Pavel Kohout of Aisle Research (www.aisle.com).

Risk Scores
Base Score
5.9

The vulnerability can be exploited over the network without needing physical access. It is difficult for an attacker to exploit this vulnerability and may require special conditions. 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
5.4

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

EPSS
0.53%

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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