CVE-2021-31999: Rancher

High severity, CVSS 8.8. EPSS: 1.1% chance of exploitation in the next 30 days.

A Reliance on Untrusted Inputs in a Security Decision vulnerability in Rancher allows users in the cluster to act as others users in the cluster by forging the "Impersonate-User" or "Impersonate-Group" headers. This issue affects: Rancher versions prior to 2.5.9. Rancher versions prior to 2.4.16.

Affected products

• Rancher Rancher: before 2.4.16 (fixed in 2.4.16); from 2.5.0, before 2.5.9 (fixed in 2.5.9)

Published 2021-07-15. Last modified 2026-06-17.