---
title: "CVE-2025-12999: Open VSX - Open Redirect & Cache Poisoning"
description: "Open VSX contains a cache poisoning vulnerability caused by unvalidated use of X-Forwarded-Host, X-Forwarded-Proto, and X-Forwarded-Prefix headers in URL construction, letting unauthenticated remote attackers inject malicious URLs into cached metadata, exploit requires a proxy that relays client headers without overwriting."
url: https://panop.io/threat-heartbeat/CVE-2025-12999/
---

# CVE-2025-12999 Open VSX - Open Redirect & Cache Poisoning

Open VSX contains a cache poisoning vulnerability caused by unvalidated use of X-Forwarded-Host, X-Forwarded-Proto, and X-Forwarded-Prefix headers in URL construction, letting unauthenticated remote attackers inject malicious URLs into cached metadata, exploit requires a proxy that relays client headers without overwriting.

CVSS base score 9.1 /10

Critical

CISA KEV

Not listed

Public exploit

None known

EPSS

0.34% chance of exploitation in 30 days

[View the NVD record ↗](https://nvd.nist.gov/vuln/detail/CVE-2025-12999)

## Details

Type

Open Redirect

Impact

Remote Code Execution

CVSS vector

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Published

21 September 2026

Updated

15 October 2026

Weakness

[CWE-345](https://cwe.mitre.org/data/definitions/345.html)

## Vendor fix

Configure proxies to overwrite X-Forwarded headers or restrict server access; update to latest version when available.

Patching closes this CVE. It does not tell you which of your systems run the affected version, or what else is exposed alongside them.

## References

- [https://nvd.nist.gov/vuln/detail/CVE-2025-12999](https://nvd.nist.gov/vuln/detail/CVE-2025-12999)
- [https://github.com/eclipse-openvsx/openvsx/security/advisories/GHSA-f55q-5m46-rmxc](https://github.com/eclipse-openvsx/openvsx/security/advisories/GHSA-f55q-5m46-rmxc)
- [https://gitlab.eclipse.org/security/cve-assignment/-/work\_items/75](https://gitlab.eclipse.org/security/cve-assignment/-/work_items/75)
- [https://github.com/eclipse-openvsx/openvsx/pull/2196](https://github.com/eclipse-openvsx/openvsx/pull/2196)

[← All CVEs](https://panop.io/threat-heartbeat/)

## What this record can't tell you

- Whether you run the affected software, and where
- Whether an attacker can actually reach and exploit it
- The misconfigurations that never get a CVE number
- What it would cost the business, ranked into what to fix first

Panop answers these inside your environment, for this CVE and every other finding.

[Book a demo](https://panop.io/demo)