<!-- There's help in the Eclipse Foundation Project Handbook https://www.eclipse.org/projects/handbook/#vulnerability-cve Note that this issue is configured (see the quick actions at the bottom) to be created as confidential. Note that a vulnerability does not need to actually be resolved before it is reported and that these reports can be revised as needed (reopen the issue to request changes). If you do not know how to fill certain fields, mark that in the comment and we will help you. You can delete the comments (or not). --> The Eclipse Foundation is a [Common Vulnerabilities and Exposures](https://cve.mitre.org/) (CVE) Numbering Authority. This issue it used to request and track the progress of the assignment of a CVE for a vulnerability in the project code for an Eclipse open source project. ## Basic information **Project name:** Eclipse Open VSX **Project id:** ecd.openvsx **Request type:** reservation **Versions affected:** [0.6.0 - 1.1.2] **Common Weakness Enumeration:** - {[CWE-349](https://cwe.mitre.org/)} - {[CWE-20](https://cwe.mitre.org/)} **Common Vulnerability Scoring System:** {[CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:L/SC:H/SI:H/SA:H](https://nvd.nist.gov/vuln-metrics/cvss)} **Title:** Cache poisoning via unvalidated X-Forwarded-Host allows attacker-controlled download URLs **Summary:** UrlUtil.getBaseUrl builds the absolute URLs in a response — download links, icons, asset and API URLs — from the X-Forwarded-Host, X-Forwarded-Proto and X-Forwarded-Prefix request headers, with no check on whether the sender was a trusted proxy, falling back to the client-supplied Host header. Those responses are cached under keys that do not include the host (extension.json since 0.6.0, namespace.details.json since 0.9.0, sitemap since 0.14.5, latest.extension.version.vscode since 0.34.2). A single request carrying a forged header therefore places attacker-chosen URLs into an entry served to every other client for the lifetime of that entry — one hour by default, and cluster-wide where ovsx.redis.enabled is set. The VSIX download URL, its signature URL and the public key URL are all derived from the same base URL, so extension signing does not limit the impact: an attacker who poisons an entry supplies the package, the signature over it, and the key used to verify it. Exploitability depends on deployment topology. A server reachable directly by clients, or fronted by a proxy that relays the client's X-Forwarded-Host rather than overwriting it, is exploitable by an unauthenticated remote attacker. A proxy that overwrites the header is not. An unauthenticated attacker can poison Open VSX's per-extension metadata cache with attacker-controlled download, signature, and public-key URLs by supplying a crafted X-Forwarded-Host header, causing downstream VS Code-compatible editors to fetch and install a malicious VSIX. **Workarounds (unpatched versions)** 1. Configure the reverse proxy to set rather than relay X-Forwarded-Host, X-Forwarded-Proto and X-Forwarded-Prefix — note that nginx's $host is the client's Host header and is not a safe value. 2. Ensure the server is not reachable except through that proxy. 3. Flush the caches afterwards; poisoned entries survive the configuration change. **Links:** - https://gitlab.eclipse.org/security/vulnerability-reports/-/issues/312 - https://github.com/eclipse-openvsx/openvsx/security/advisories/GHSA-f55q-5m46-rmxc - https://github.com/eclipse-openvsx/openvsx/pull/2196 ## Tracking **This section will completed by the project team**. - [x] Reserve an entry only - [ ] We're ready for this issue to be reported to the central authority (i.e., make this public now) - [ ] (when applicable) The GitHub Security Advisory is ready to be published now Note that for those projects that host their repositories on GitHub, the use of GitHub Security Advisories is recommended but is not required. **This section will be completed by the EMO**. **CVE:** CVE-2025-12999 - [ ] All required information is provided - [ ] CVE Assigned - [ ] Pushed to Mitre - [ ] Accepted by Mitre <!-- Quick actions will configure the state of the issue. Leave these. -->