CVE-2021-31999 is a high-severity security vulnerability in github.com/rancher/rancher (go), affecting versions >= 2.0.0, < 2.4.16. It is fixed in 2.4.16, 2.5.9.
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.
CVE-2021-31999 has a CVSS score of 8.8 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment.
A fixed version is available (2.4.16, 2.5.9). Upgrading removes the vulnerable code path.
go
github.com/rancher/rancher (>= 2.0.0, < 2.4.16)github.com/rancher/rancher (>= 2.5.0, < 2.5.9)github.com/rancher/rancher → 2.4.16 (go)github.com/rancher/rancher → 2.5.9 (go)Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter instead of chasing every advisory.
Kodem's runtime-powered SCA identifies whether CVE-2021-31999 is reachable in your applications. Explore open-source security for your team.
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Already deployed Kodem? See CVE-2021-31999 in your environment →Upgrade the following packages to resolve this vulnerability:
github.com/rancher/rancher to 2.4.16 or latergithub.com/rancher/rancher to 2.5.9 or laterKodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
CVE-2021-31999 is a high-severity security vulnerability in github.com/rancher/rancher (go), affecting versions >= 2.0.0, < 2.4.16. It is fixed in 2.4.16, 2.5.9.
CVE-2021-31999 has a CVSS score of 8.8 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
github.com/rancher/rancher (go) versions >= 2.0.0, < 2.4.16 is affected.
Yes. CVE-2021-31999 is fixed in 2.4.16, 2.5.9. Upgrade to this version or later.
Whether CVE-2021-31999 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
github.com/rancher/rancher to 2.4.16 or latergithub.com/rancher/rancher to 2.5.9 or later