Eclipse Open VSX up to 1.1.2 UrlUtil UrlUtil.getBaseUrl input validation

Summaryinfo

A vulnerability described as problematic has been identified in Eclipse Open VSX up to 1.1.2. The affected element is the function UrlUtil.getBaseUrl of the component UrlUtil. The manipulation of the argument X-Forwarded-Host/X-Forwarded-Proto/X-Forwarded-Prefix results in input validation. This vulnerability is cataloged as CVE-2025-12999. The attack may be launched remotely. There is no exploit available.

Detailsinfo

A vulnerability was found in Eclipse Open VSX up to 1.1.2. It has been classified as problematic. Affected is the function UrlUtil.getBaseUrl of the component UrlUtil. The manipulation of the argument X-Forwarded-Host/X-Forwarded-Proto/X-Forwarded-Prefix with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on integrity. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability is traded as CVE-2025-12999 since 11/11/2025. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/21/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• Eclipse

Name

• Open VSX

Version

• 1.1.0
• 1.1.1
• 1.1.2

License

• open-source

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