# CVE-2026-89058: Resteasy-core: resteasy: corsfilter reflects arbitrary origin with credentials under wildcard config

> RESTEasy's CorsFilter reflects arbitrary origins with credentials when configured with wildcard, allowing malicious sites to read authenticated responses.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 18 Sep 2026
- **Updated:** 29 Oct 2026
- **Also known as:** CLEANSTART-2026-KS26010, CLEANSTART-2026-ZN77220, DEBIAN-CVE-2026-89058, GHSA-972r-f3fv-whm3, OESA-2026-4304, OESA-2026-4305, OESA-2026-4306, OESA-2026-4307, UBUNTU-CVE-2026-89058

## What is CVE-2026-89058?

CVE-2026-89058 is a high-severity vulnerability in Red Hat Build of Keycloak, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

A flaw was found in RESTEasy's CorsFilter, which, when configured to allow all origins ("*"), reflects the request's Origin header back in the Access-Control-Allow-Origin response together with Access-Control-Allow-Credentials: true. This permissive cross-origin policy allows a malicious website to make credentialed cross-origin requests and read authenticated responses from a victim's session, resulting in a loss of confidentiality.

Weakness: CWE-942 (Permissive Cross-domain Security Policy with Untrusted Domains), CWE-346 (Origin Validation Error)

## Which versions are affected by CVE-2026-89058?


## How do I fix CVE-2026-89058?

Apply the vendor's patch.

## Is CVE-2026-89058 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89058 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-89058 and fix it if it is affected.

What it is: CVE-2026-89058 is a high-severity vulnerability in Red Hat Build of Keycloak, published on 18 Sep 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89058 exists.

Affected product: Red Hat Build of Keycloak. 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-2026-89058/ (Markdown: https://insights.sbomify.com/CVE-2026-89058/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-89058
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-89058
- OSV: https://osv.dev/vulnerability/CVE-2026-89058

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-89058/
Summaries are generated and may contain mistakes; the official description above is the record.