---
title: "CVE-2026-23518: Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment"
url: https://erroneo.us/security/cve/CVE-2026-23518/
description: "CVE-2026-23518 (github.com/fleetdm/fleet (Go)): Fleet is open source device management software. In versions prior to 4.78.3, 4.77.1, 4.76.2, 4.75.2, and…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-01-21
date_modified: 2026-03-27
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-23518"
kev: false
cvss: 9.3
epss: 0.00254
license: All rights reserved. Quote with attribution and a link.
---

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

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.3% , percentile 16: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 16% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes github.com/fleetdm/fleet (Go) >= 4.78.0, < 4.78.3, fixed in 4.78.3 ; github.com/fleetdm/fleet (Go) >= 4.77.0, < 4.77.1, fixed in 4.77.1 ; github.com/fleetdm/fleet (Go) >= 4.76.0, < 4.76.2, fixed in 4.76.2 ; github.com/fleetdm/fleet (Go) >= 4.75.0, < 4.75.2, fixed in 4.75.2 . Check your lockfile, including transitive dependencies.

## What it is

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.

## Affected packages

- Go `github.com/fleetdm/fleet` >= 4.78.0, < 4.78.3 → fixed: 4.78.3
- Go `github.com/fleetdm/fleet` >= 4.77.0, < 4.77.1 → fixed: 4.77.1
- Go `github.com/fleetdm/fleet` >= 4.76.0, < 4.76.2 → fixed: 4.76.2
- Go `github.com/fleetdm/fleet` >= 4.75.0, < 4.75.2 → fixed: 4.75.2
- Go `github.com/fleetdm/fleet` < 4.43.5-0.20260112202845-e225ef57912c → fixed: 4.43.5-0.20260112202845-e225ef57912c

## Affected products (CVE record)

- fleetdm fleet: >= 4.78.0, < 4.78.3, >= 4.77.0, < 4.77.1, >= 4.76.0, < 4.76.2, >= 4.75.0, < 4.75.2, < 4.53.3

## Severity

- GitHub_M CVSS 4.0: 9.3 `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`
- GitHub CVSS 4.0: 9.3 `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`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 0.25% probability of exploitation activity in the next 30 days; percentile 16.

## Sources

- [GitHub Advisory GHSA-63m5-974w-448v](https://github.com/advisories/GHSA-63m5-974w-448v)
- [CVE.org record CVE-2026-23518](https://www.cve.org/CVERecord?id=CVE-2026-23518)
- [NVD entry CVE-2026-23518](https://nvd.nist.gov/vuln/detail/CVE-2026-23518)
- [github.com](https://github.com/fleetdm/fleet/security/advisories/GHSA-63m5-974w-448v)
- [github.com](https://github.com/fleetdm/fleet/commit/e225ef57912c8f4ac8977e24b5ebe1d9fd875257)
- [pkg.go.dev](https://pkg.go.dev/vuln/GO-2026-4335)

---
Source page: https://erroneo.us/security/cve/CVE-2026-23518/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt