CVE-2021-31999 — rancher
HIGHCVE-2021-31999 is a high-severity (CVSS 8.8) CWE-807 vulnerability in github.com/rancher/rancher. A fix is available for github.com/rancher/rancher — see the affected versions and patch details below.
Rancher Privilege escalation vulnerability via malicious "Connection" header
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
github.com/rancher/rancher🐹github.com/rancher/rancherReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
A vulnerability was discovered in Rancher 2.0.0 through the aforementioned patched versions, where a malicious Rancher user could craft an API request directed at the proxy for the Kubernetes API of a managed cluster to gain access to information they do not have access to. This is done by passing the "Impersonate-User" or "Impersonate-Group" header in the Connection header, which is then correctly removed by the proxy. At this point, instead of impersonating the user and their permissions, the request will act as if it was from the Rancher management server and incorrectly return the information. The vulnerability is limited to valid Rancher users with some level of permissions on the cluster. There is not a direct mitigation besides upgrading to the patched Rancher versions.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/rancher/rancher | ≥ 2.0.0&&< 2.4.16 | 2.4.16go get github.com/rancher/rancher@v2.4.16 |
| 🐹Go | github.com/rancher/rancher | ≥ 2.5.0&&< 2.5.9 | 2.5.9go get github.com/rancher/rancher@v2.5.9 |
Affected Products
rancherrancherDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/rancher/rancher, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/rancher/rancher to 2.4.16 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-31999 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
Frequently Asked Questions
Is CVE-2021-31999 in your dependencies?
Find it across Go, including transitive dependencies.