CVE-2021-31999Network attack vector

Authenticated privilege escalation via proxy header stripping

Published Jul 15, 2021 · Updated Sep 17, 2024

Privilege escalation in Rancher 2.0.0 through 2.4.15 and 2.5.0 through 2.5.8 allows remote authenticated users to read unauthorized cluster data. The Kubernetes API proxy strips forged Impersonate-User or Impersonate-Group headers when the Connection header marks them as hop-by-hop, then processes the request under the Rancher management server's identity instead of the caller's permissions. A valid Rancher account with some cluster permissions is required; successful requests expose information beyond that account's authorization.

CVSS severity8.8
High
EPSS probability1.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Privilege escalation in Rancher 2.0.0 through 2.4.15 and 2.5.0 through 2.5.8 allows remote authenticated users to read unauthorized cluster data. The Kubernetes API proxy strips forged Impersonate-User or Impersonate-Group headers when the Connection header marks them as hop-by-hop, then processes the request under the Rancher management server's identity instead of the caller's permissions. A valid Rancher account with some cluster permissions is required; successful requests expose information beyond that account's authorization.

The record

CVE
CVE-2021-31999
Published
Jul 15, 2021
Updated
Sep 17, 2024
Vendor
Rancher
Product
Rancher
Classifications
CWE-807, T1078
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Jul 15, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Rancher <2.5.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Rancher · Rancherversion=Rancher <2.5.9

Published CVSS scores

8.8NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.7GitHubCVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
8.8SUSECVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
6.5NVDAV:N/AC:L/Au:S/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-807Reliance on Untrusted Inputs in a Security Decision
T1078Valid Accounts

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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