How severe is CVE-2026-23518?

No CVSS score has been assigned to CVE-2026-23518 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-23518?

CVE-2026-23518 affects the following packages: github.com/fleetdm/fleet (Go), github.com/fleetdm/fleet (Go), github.com/fleetdm/fleet (Go), github.com/fleetdm/fleet (Go), github.com/fleetdm/fleet (Go). Ecosystems affected: Go.

How do I fix CVE-2026-23518?

Update github.com/fleetdm/fleet to 4.78.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23518 is resolved across your whole dependency graph.

How do I detect CVE-2026-23518 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/fleetdm/fleet, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-23518 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2026-23518 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-23518 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-23518?

CVE-2026-23518 has an EPSS (Exploit Prediction Scoring System) score of 0.3%, placing it in the 17th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-23518?

CVE-2026-23518 is classified as CWE-347 (CWE-347). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-23518 published, and has it been updated?

CVE-2026-23518 was published on January 21, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-23518 — fleet

Fix: fleetdm/fleet@e225ef5

CVE-2026-23518 is a CWE-347 vulnerability in github.com/fleetdm/fleet. A fix is available for github.com/fleetdm/fleet — see the affected versions and patch details below.

Fleet has a JWT signature bypass vulnerability in Azure AD MDM enrollment

Also known asGHSA-63m5-974w-448vGO-2026-4335

Published

Jan 21, 2026

Updated

Oct 28, 2026

Affected

5 pkgs

Patched

5 / 5

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-23518.

EPSS Exploitation Probability

via FIRST.org ↗

0.3%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs17th percentile — riskier than 17% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

5 pkgs affected

🐹github.com/fleetdm/fleet🐹github.com/fleetdm/fleet🐹github.com/fleetdm/fleet🐹github.com/fleetdm/fleet🐹github.com/fleetdm/fleet

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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 [email protected] Join #fleet in osquery Slack

Credits

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

Affected Packages

5 total 5 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/fleetdm/fleet`	≥ 4.78.0&&< 4.78.3	4.78.3`go get github.com/fleetdm/fleet@v4.78.3`
🐹Go	`github.com/fleetdm/fleet`	≥ 4.77.0&&< 4.77.1	4.77.1`go get github.com/fleetdm/fleet@v4.77.1`
🐹Go	`github.com/fleetdm/fleet`	≥ 4.76.0&&< 4.76.2	4.76.2`go get github.com/fleetdm/fleet@v4.76.2`
🐹Go	`github.com/fleetdm/fleet`	≥ 4.75.0&&< 4.75.2	4.75.2`go get github.com/fleetdm/fleet@v4.75.2`
🐹Go	`github.com/fleetdm/fleet`	all versions	4.43.5-0.20260112202845-e225ef57912c`go get github.com/fleetdm/fleet@v4.43.5-0.20260112202845-e225ef57912c`

Affected Products

1 product · 5 configurations

Application

fleetfleetdm

≥ 4.78.0 && < 4.78.3

1 version

4.77.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/fleetdm/fleet, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/fleetdm/fleet to 4.78.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-23518 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### 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 is