# CVE-2026-21588: Denial of service in Confluence Data Center

> An authenticated attacker can cause a denial of service in Confluence Data Center, disrupting availability for intended users.

- **Severity:** High 7.1 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Sep 2026
- **Updated:** 15 Sep 2026
- **Also known as:** GHSA-4848-75hf-436m

## What is CVE-2026-21588?

CVE-2026-21588 is a high-severity denial of service vulnerability in Atlassian Confluence Data Center, published on 15 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

This High severity DoS (Denial of Service) vulnerability was introduced in versions 8.9.0, 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 9.2.24

 Confluence Data Center 10.2: Upgrade to a release greater than or equal to 10.2.17

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.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2026-21588?


## How do I fix CVE-2026-21588?

No fix has been published for CVE-2026-21588 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-21588 being exploited?

There is no known exploitation of CVE-2026-21588 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21588 and fix it if it is affected.

What it is: CVE-2026-21588 is a high-severity denial of service vulnerability in Atlassian Confluence Data Center, published on 15 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-21588 in the wild and no public exploit code.

Affected product: Atlassian Confluence Data Center. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-21588/ (Markdown: https://insights.sbomify.com/CVE-2026-21588/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21588
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21588
- OSV: https://osv.dev/vulnerability/CVE-2026-21588

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21588/
Summaries are generated and may contain mistakes; the official description above is the record.