CVE-2026-34388 — v4
CVE-2026-34388 is a CWE-703 vulnerability in github.com/fleetdm/fleet/v4. A fix is available for github.com/fleetdm/fleet/v4 — see the affected versions and patch details below.
Fleet vulnerable to Denial of Service via unhandled gRPC log type in launcher endpoint
Exploitation Status
No confirmed exploitation observed yet
- 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-2026-34388.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
Real-World Exposure
github.com/fleetdm/fleet/v4Real-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 Denial of Service vulnerability in Fleet's gRPC Launcher endpoint allows an authenticated host to crash the entire Fleet server process by sending an unexpected log type value. The server terminates immediately, disrupting all connected hosts, MDM enrollments, and API consumers.
Impact
An attacker with access to a valid Launcher node key can send a specially crafted gRPC request to the Fleet server that triggers an unrecoverable server crash. The gRPC server lacks appropriate error recovery handling, meaning the entire Fleet process terminates rather than gracefully rejecting the malformed input.
Because the crash is instant and repeatable, an attacker could script repeated requests to prevent the server from recovering, resulting in a persistent denial of service until a patched version is deployed.
Workarounds
There is no workaround for this issue other than upgrading to a patched version.
For more information
If there are any questions or comments about this advisory:
Send an email to [email protected]
Join #fleet in osquery Slack
Credits
Fleet thanks @fuzzztf for responsibly reporting this issue.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/fleetdm/fleet/v4 | all versions | 4.81.0go get github.com/fleetdm/fleet/v4@v4.81.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/fleetdm/fleet/v4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/fleetdm/fleet/v4 to 4.81.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-34388 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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-34388 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-34388. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-34388 in your dependencies?
O3 Security finds CVE-2026-34388 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.