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NVD / CVE Program· CNA suse

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

HighCVSS 8.8 · v3.1—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 35/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 1% (FIRST EPSS); higher than 64.7% of all records.
  • Anyone who can reach it over the internet can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: github.com/rancher/rancher (Go) 2.4.16, 2.5.9.

Low priority for now. Upgrade to github.com/rancher/rancher (Go) 2.4.16, 2.5.9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Published
Jul 15, 2021
Updated
Jun 16, 2026
EPSS
1.0% · 64th percentile

Report tools

JSON

Action score

35

Monitor

Low priority for now.

CVSS
35 / 40 · 8.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 1.0%

CNA vs NVD score

NVD
8.8
CNA · suse
8.8
agree

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
rancherrancher

Versions reported by the vendor

Affected version ranges reported by the assigning authority (suse). Independent of NVD's CPE analysis and usually ahead of it.

  • Rancher Rancher

    • Rancher and later · before 2.5.9affected

  • Rancher SUSE Linux Enterprise Server 15

    • Rancher and later · before 2.4.16affected

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • rancher rancherbefore 2.4.16
  • rancher rancher2.5.0 and later · before 2.5.9

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Gogithub.com/rancher/rancherfrom 2.0.0 · before 2.4.162.4.16
Gogithub.com/rancher/rancherfrom 2.0.0+incompatible—
Gogithub.com/rancher/rancherfrom 2.5.0 · before 2.5.92.5.9

Same product

rancher: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-25320Rancher: Cloud credentials can be used through proxy API by users without access
    39Monitor
  • CVE-2026-55997Long-lived Rancher registration token exposed in plaintext
    35Monitor
  • CVE-2021-36776Steve API proxy impersonation
    35Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2021-25318Jul 15, 2021 · rancher: API group not properly specified when creating Kubernetes RBAC resources
    35Monitor
  • Later →CVE-2021-36775Apr 4, 2022 · Deleting PRTBs associated to a group doesn't cause deletion of corresponding RoleBindings
    35Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Go:github.com/rancher/rancher2.4.16Package registry (OSV)
Go:github.com/rancher/rancher2.5.9Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

Not on record for this CVE: EPSS history · patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-807 · Reliance on Untrusted Inputs in a Security Decision

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records