CVE-2021-31999

Q: How do I fix CVE-2021-31999?

Upgrade rancher to 2.5.9 or later.

Q: Is CVE-2021-31999 being actively exploited?

Not that we know of. CVE-2021-31999 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.1% is the estimated probability that it will be exploited in the next 30 days. That is higher than 61% of all scored CVEs.

Q: How severe is CVE-2021-31999?

CVE-2021-31999 has a CVSS v3 base score of 8.8, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

Q: What does CVE-2021-31999 affect?

Published advisories record a fix for rancher (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

HIGH

8.8

CVSS v3

NVD

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.

CWE-807

How to fix

Remediation Available

rancherNVD

Affected:>= 2.5.0, < 2.5.9Fixed in:2.5.9CVE-2021-31999derived from NVD

TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredLow

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityHigh

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Exploit Intelligence

1.05%probability of exploitation in 30 days

61stpercentile

Moderate risk: more likely to be exploited than 61% of all known CVEs.

References

Third-Party Advisory1

bugzilla.suse.com

Related Vulnerabilities

Other CWE-807 vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2026-34486	High	7.5	81%	KEV	Fix
CVE-2026-21509	High	7.8	72%	KEV	Fix
CVE-2024-13974	High	8.1	6.7%	-	Fix
CVE-2021-41129	High	8.1	1.8%	-	Fix
CVE-2026-21514	High	7.8	1.5%	KEV	-
CVE-2025-49827	Critical	9.8	1.4%	-	Fix

Common questions

How do I fix CVE-2021-31999?

Upgrade rancher to 2.5.9 or later.

Is CVE-2021-31999 being actively exploited?

Not that we know of. CVE-2021-31999 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 1.1% is the estimated probability that it will be exploited in the next 30 days. That is higher than 61% of all scored CVEs.

How severe is CVE-2021-31999?

CVE-2021-31999 has a CVSS v3 base score of 8.8, rated high. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.

What does CVE-2021-31999 affect?

Published advisories record a fix for rancher (NVD). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2024-11-21.