CVE-2026-40211
Deferred Deferred - Pending Action
DNS over HTTP/3 Memory Leak DoS Vulnerability

Publication date: 2026-06-25

Last updated on: 2026-06-25

Assigner: Open-Xchange

Description
An attacker can send crafted DNS over HTTP/3 queries, triggering an exception that prevents some buffer from being freed right away. The buffer will be freed at the end of the QUIC connection, but on some setups it might be possible to open enough concurrent DoH3 streams to trigger an out-of-memory condition, resulting in a denial of service.
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Meta Information
Published
2026-06-25
Last Modified
2026-06-25
Generated
2026-06-25
AI Q&A
2026-06-25
EPSS Evaluated
N/A
NVD
CVE-2026-40211
EUVD
EUVD-2026-39350
Affected Vendors & Products
Currently, no data is known.
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Exploitability
CWE
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KEV
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CWE ID Description
CWE-770 The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
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Executive Summary

This vulnerability involves an attacker sending specially crafted DNS queries over HTTP/3 (DoH3) that trigger an exception in the system. This exception prevents a certain buffer from being freed immediately. Although the buffer is eventually freed at the end of the QUIC connection, on some setups, an attacker can open enough concurrent DoH3 streams to exhaust memory resources.

The result is an out-of-memory condition that can cause the system to become unresponsive or crash, leading to a denial of service.

Impact Analysis

The primary impact of this vulnerability is a denial of service (DoS). An attacker can exploit it to consume system memory by opening many concurrent DNS over HTTP/3 streams, causing the system to run out of memory.

This can lead to service interruptions, crashes, or degraded performance, affecting availability of the affected service or application.

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