GHSA-63M5-974W-448V

Vulnerability from github – Published: 2026-01-20 20:55 – Updated: 2026-01-22 15:39
VLAI?
Summary
Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment
Details

Summary

A vulnerability in Fleet’s Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities.

Impact

If Windows MDM is enabled, an attacker can enroll rogue devices by submitting a forged JWT containing arbitrary identity claims. Due to missing JWT signature verification, Fleet accepts these claims without validating that the token was issued by Azure AD, allowing enrollment under any Azure AD user identity.

Patches

  • 4.78.3
  • 4.77.1
  • 4.76.2
  • 4.75.2
  • 4.53.3

Workarounds

If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.

For more information

If you have any questions or comments about this advisory:

Email us at security@fleetdm.com Join #fleet in osquery Slack

Credits

We thank @secfox-ai for responsibly reporting this issue.

Severity ?
9.3 (Critical)
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
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{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fleetdm/fleet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.78.0"
            },
            {
              "fixed": "4.78.3"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fleetdm/fleet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.77.0"
            },
            {
              "fixed": "4.77.1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fleetdm/fleet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.76.0"
            },
            {
              "fixed": "4.76.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fleetdm/fleet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.75.0"
            },
            {
              "fixed": "4.75.2"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/fleetdm/fleet"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4.43.5-0.20260112202845-e225ef57912c"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-23518"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-347"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-01-20T20:55:17Z",
    "nvd_published_at": "2026-01-21T22:15:50Z",
    "severity": "CRITICAL"
  },
  "details": "### Summary\n\nA vulnerability in Fleet\u2019s Windows MDM enrollment flow could allow an attacker to submit forged authentication tokens that are not properly validated. Because JWT signatures were not verified, Fleet could accept attacker-controlled identity claims, enabling enrollment of unauthorized devices under arbitrary Azure AD user identities.\n\n### Impact\n\nIf Windows MDM is enabled, an attacker can enroll rogue devices by submitting a forged JWT containing arbitrary identity claims. Due to missing JWT signature verification, Fleet accepts these claims without validating that the token was issued by Azure AD, allowing enrollment under any Azure AD user identity.\n\n### Patches\n\n- 4.78.3\n- 4.77.1\n- 4.76.2\n- 4.75.2\n- 4.53.3\n\n### Workarounds\n\nIf an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.\n\n### For more information\n\nIf you have any questions or comments about this advisory:\n\nEmail us at [security@fleetdm.com](mailto:security@fleetdm.com)\nJoin #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)\n\n### Credits\n\nWe thank @secfox-ai for responsibly reporting this issue.",
  "id": "GHSA-63m5-974w-448v",
  "modified": "2026-01-22T15:39:04Z",
  "published": "2026-01-20T20:55:17Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/fleetdm/fleet/security/advisories/GHSA-63m5-974w-448v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-23518"
    },
    {
      "type": "WEB",
      "url": "https://github.com/fleetdm/fleet/commit/e225ef57912c8f4ac8977e24b5ebe1d9fd875257"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/fleetdm/fleet"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment "
}


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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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