What is CVE-2026-77900?

CVE-2026-77900 is a critical-severity vulnerability in Microsoft Azure App Service For Linux, classified under Missing Authentication for Critical Function. CVSS score: 9.8/10. Published 2026-10-08.

How severe is CVE-2026-77900?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Auth bypass in Microsoft Azure App Service For Linux

CVE-2026-77900

Missing authentication for critical function in Azure App Service allows an unauthorized attacker to execute code over a network.

Vulnerability class: Broken Authentication

Published 2026-10-08 · last modified 2026-10-09.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.

Affected products

Microsoft Azure App Service For Linux

Weakness classification (CWE)

CWE-306 — Missing Authentication for Critical Function

References

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-77900 (vendor-advisory, patch)

Frequently asked questions

What is CVE-2026-77900?: CVE-2026-77900 is a critical-severity vulnerability in Microsoft Azure App Service For Linux, classified under Missing Authentication for Critical Function. CVSS score: 9.8/10. Published 2026-10-08.
How severe is CVE-2026-77900?: Critical severity. CVSS v3 base score is 9.8 out of 10.