What is CVE-2026-21577?

CVE-2026-21577 is a medium-severity vulnerability in Atlassian Confluence Data Center, classified under Uncontrolled Resource Consumption. CVSS score: 6.5/10. Published 2026-07-21.

How severe is CVE-2026-21577?

Medium severity. CVSS v3 base score is 6.5 out of 10.

Resource exhaustion in Atlassian Confluence Data Center

CVE-2026-21577

This High severity DoS (Denial of Service) vulnerability was introduced in versions 9.0.1, 9.1.0, 9.2.0, 9.3.1, 9.4.0, 9.5.1, 10.0.2, 10.1.0 and 10.2.0 of Confluence Data Center. This DoS (Denial of Service) vulnerability, with a CVSS Score of 7.1, allows an authenticated attacker to cause a resource to be unavailable for its intended users by temporarily or indefinitely disrupting services of a host connected to a network. Atlassian recommends that Confluence Data Center customers upgrade to latest version, if you are unable to do so, upgrade your instance to one of the specified supported fixed versions: Confluence Data Center 9.2: Upgrade to a release greater than or equal to 9.2.17 Confluence Data Center 10.2: Upgrade to a release greater than or equal to 10.2.7 See the release notes ([https://confluence.atlassian.com/doc/confluence-release-notes-327.html]). You can download the latest version of Confluence Data Center from the download center ([https://www.atlassian.com/software/confluence/download-archives]). This vulnerability was reported via our Penetration Testing program.

Vulnerability class: DoS (Denial of Service)

Published 2026-07-21 · last modified 2026-08-10.

CVSS v3 metric

CVSS v3 base score 6.5 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.004 (35.8th percentile), scored 2026-10-22.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.002 · newest: 0.004 · change: +0.002

Affected products

Atlassian Confluence Data Center — versions 10.2.0 to 10.2.6, 10.1.0 to 10.1.2, 10.0.2 to 10.0.3
Atlassian Confluence Data Center

Weakness classification (CWE)

CWE-400 — Uncontrolled Resource Consumption

References

confluence.atlassian.com/pages/viewpage.action (Vendor Advisory)
jira.atlassian.com/browse/CONFSERVER-104334 (Issue Tracking)

Frequently asked questions

What is CVE-2026-21577?: CVE-2026-21577 is a medium-severity vulnerability in Atlassian Confluence Data Center, classified under Uncontrolled Resource Consumption. CVSS score: 6.5/10. Published 2026-07-21.
How severe is CVE-2026-21577?: Medium severity. CVSS v3 base score is 6.5 out of 10.