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» CVE-2021-31999
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.
NVD Status： Modified ，CVE State: published
Threat Intelligence & Risk Assessment for CVE-2021-31999
Conclusion & alert: CVE-2021-31999 is rated Moderate Risk (56.8/100) : CVSS High severity, with medium exploitation likelihood (EPSS 1.05%).Mandatory action: Review affected assets and schedule remediation.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
Exploit prediction scoring system (EPSS) score for CVE-2021-31999
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
#
Date
Old EPSS score
New EPSS score
Delta (New - Old)
1
2026-06-15
0.35%
1.05%
+0.70%
2
2025-03-30
0.69%
0.35%
-0.33%
3
2025-03-29
—
0.69%
—
Full EPSS history
(9 records total)
Common vulnerability scoring system (CVSS) metrics for CVE-2021-31999
CVSS metrics for this CVE.
Base score
Version
Severity
Vector
Exploitability
Impact
Score source
8.8
3.1
HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
2.8
5.9
[email protected]
8.8
3.1
HIGH
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
2.8
5.9
[email protected]
6.5
2.0
MEDIUM
AV:N/AC:L/Au:S/C:P/I:P/A:P
Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
8.0
6.4
[email protected]
Weakness enumeration for CVE-2021-31999
GitHub Security Advisory for CVE-2021-31999
GHSA-pvxj-25m6-7vqr · Severity: high · Ecosystem: go
— Rancher Privilege escalation vulnerability via malicious "Connection" header
OS Trackers for CVE-2021-31999
Affected software / configurations for CVE-2021-31999
Vendor
Product
Version
Raw CPE
rancher
rancher
< 2.4.16
cpe:2.3:a:rancher:rancher:*:*:*:*:*:*:*:*
rancher
rancher
>= 2.5.0, < 2.5.9
cpe:2.3:a:rancher:rancher:*:*:*:*:*:*:*:*
References for CVE-2021-31999
cvelogic
Threat Intelligence