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 ↗

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

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

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