CVE-2026-40691: Packet of death for DNSCrypt over TCP

CSIRTS triage

What

A vulnerability known as 'Packet of death' affects DNSCrypt over TCP.

Who is affected

Deployments using DNSCrypt over TCP are affected.

Urgency

Remediation is urgent due to the high severity of the vulnerability.

Action

Apply patches or mitigations as soon as they are available.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source

Microsoft Security Response Center (INTL · vendor-psirt · site)

Severity

high — CVSS 7.5

Published

2026-07-14

Exploitation

Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40691

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

• Low exploitation riskCVE-2026-406910.29% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 22% of all scored CVEs.

Referenced CVEs

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

• medium[NEW] [medium] Unbound: Multiple vulnerabilitiescert-bund
• highCVE-2026-40691: In Unbound 1.9.0 up to and including 1.25.1, when a DNSCrypt query is received over TCP, the r…nvd

More from Microsoft Security Response Center

• highCVE-2026-57992: Microsoft Edge (Chromium-based) Remote Code Execution Vulnerability2026-07-14
• mediumCVE-2026-59926: Mistune: XSS via unescaped class option in Admonition directive2026-07-14
• mediumCVE-2026-55003: Windows Remote Desktop Protocol (RDP) Information Disclosure Vulnerability2026-07-14
• highCVE-2026-42900: Microsoft Windows App Store Elevation of Privilege Vulnerability2026-07-14
• unknownCVE-2026-13867: Chromium: CVE-2026-13867 Inappropriate implementation in Geolocation2026-07-14