What is CVE-2026-55991?

CVE-2026-55991 is a security advisory published by Microsoft Security Response Center (MSRC) with Medium severity. Remote DNS-over-QUIC (DoQ) flow-control assertion failure in libngtcp2

Which CVE IDs does CVE-2026-55991 cover?

CVE-2026-55991 covers the following CVE IDs: CVE-2026-55991. Each CVE has its own detail page on EchelonGraph Pulse with the synthesized EG score.

What is the CVSS v3 score of CVE-2026-55991?

CVE-2026-55991 has a CVSS v3 base score of 5.9, published by Microsoft Security Response Center (MSRC).

Which products are affected by CVE-2026-55991?

CVE-2026-55991 affects 1 product, including: azl3 unbound 1.25.1-1 on Azure Linux 3.0.

CVE-2026-55991MediumCVSS 5.9

Remote DNS-over-QUIC (DoQ) flow-control assertion failure in libngtcp2

Vendor

Microsoft Security Response Center (MSRC)

Published

July 23, 2026

Last Modified

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🔗 CVE IDs covered (1)

CVE-2026-55991 →

🎯 Affected products1

azl3 unbound 1.25.1-1 on Azure Linux 3.0

✅ Remediation

KBCBL-Mariner Releases (Security Update) — fixed build 1.25.2-1

🔗 References (2)

advisoryhttps://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55991
referencehttps://learn.microsoft.com/en-us/azure/azure-linux/tutorial-azure-linux-upgrade