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CVE-2021-25735

Status: ModifiedMedium (6.5)—💥 PoC

A security issue was discovered in kube-apiserver that could allow node updates to bypass a Validating Admission Webhook. Clusters are only affected by this vulnerability if they run a Validating Admission Webhook for Nodes that denies admission based at least partially on the old state of the Node object. Validating Admission Webhook does not observe some previous fields.

CVSS

Exploitation probability (EPSS)

EPSS (Exploit Prediction Scoring System, FIRST) estimates how likely a vulnerability is to be exploited in the wild within 30 days. It complements CVSS (impact) and CISA KEV (confirmed exploitation).

💥 Public exploits

Exploit code or detection templates are publicly available. This is not the same as confirmed active exploitation (KEV), but it raises the risk: patch with priority.

⚠️ GitHub proofs of concept are not verified: some are fake or contain malware. Never run them outside an isolated lab.

Affected technologies (1)

Kubernetes — Kubernetes

CWEs

References

Raw JSON (NVD)

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{
  "id": "CVE-2021-25735",
  "cveTags": [],
  "metrics": {
    "cvssMetricV2": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
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          "baseScore": 5.5,
          "accessVector": "NETWORK",
          "vectorString": "AV:N/AC:L/Au:S/C:N/I:P/A:P",
          "authentication": "SINGLE",
          "integrityImpact": "PARTIAL",
          "accessComplexity": "LOW",
          "availabilityImpact": "PARTIAL",
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        "obtainAllPrivilege": false,
        "exploitabilityScore": 8,
        "obtainUserPrivilege": false,
        "obtainOtherPrivilege": false,
        "userInteractionRequired": false
      }
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    "cvssMetricV31": [
      {
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        "source": "jordan@liggitt.net",
        "cvssData": {
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          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:H/A:H",
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          "privilegesRequired": "HIGH",
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      "affectedData": [
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          "vendor": "Kubernetes",
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          "versions": [
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  "published": "2021-09-06T12:15:07.617",
  "references": [
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      "tags": [
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  "vulnStatus": "Modified",
  "weaknesses": [
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      "description": [
        {
          "lang": "en",
          "value": "CWE-372"
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    {
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      "description": [
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  "descriptions": [
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      "value": "A security issue was discovered in kube-apiserver that could allow node updates to bypass a Validating Admission Webhook. Clusters are only affected by this vulnerability if they run a Validating Admission Webhook for Nodes that denies admission based at least partially on the old state of the Node object. Validating Admission Webhook does not observe some previous fields."
    },
    {
      "lang": "es",
      "value": "Se ha detectado un problema de seguridad en kube-apiserver que podría permitir a las actualizaciones de los nodos omitir un Validating Admission Webhook. Los clusters sólo están afectados por esta vulnerabilidad si ejecutan un Validating Admission Webhook para nodos que deniega la admisión basándose, al menos parcialmente, en el estado antiguo del objeto Node. El Validating Admission Webhook no comprueba algunos campos anteriores."
    }
  ],
  "lastModified": "2026-06-17T03:42:22.503",
  "configurations": [
    {
      "nodes": [
        {
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          "cpeMatch": [
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          ],
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  "sourceIdentifier": "jordan@liggitt.net"
}