CVE-2026-34388: Github.com/fleetdm/fleet/v4 Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-w254-4hp5-7cvv
Share
CWE-703
Published
Advisory Summary

CVE-2026-34388 is a MODERATE denial of service vulnerability (CWE-703: Improper Check or Handling of Exceptional Conditions) affecting Github.com/fleetdm/fleet/v4 libraries in the Go ecosystem. The issue involves fleet vulnerable to denial of service via unhandled grpc log type in launcher endpoint. Remediation is available by upgrading affected packages to version 4.81.0.

CVE-2026-34388 at a Glance

CVE Identifier CVE-2026-34388
GHSA Identifier GHSA-w254-4hp5-7cvv
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-703: Improper Check or Handling of Exceptional Conditions
Affected Product Github.com/fleetdm/fleet/v4
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-34388

To remediate this vulnerability, upgrade all affected Github.com/fleetdm/fleet/v4 dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/fleetdm/fleet/v4 fixed: 4.81.0 
Upgrade github.com/fleetdm/fleet/v4 to 4.81.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/fleetdm/fleet/v4

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-34388, inspect your project dependencies for Github.com/fleetdm/fleet/v4:

inspect dependencies for github.com/fleetdm/fleet/v4

Analyze the terminal output to locate any version of Github.com/fleetdm/fleet/v4 in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 4.81.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-703: Improper Check or Handling of Exceptional Conditions, where the product does not properly anticipate or handle exceptional conditions that rarely occur during normal operation of the product. In Github.com/fleetdm/fleet/v4, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### 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 [security@fleetdm.com](mailto:security@fleetdm.com) Join #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw) ### Credits Fleet thanks @fuzzztf for responsibly reporting this issue.

CVE-2026-34388 Affected Github.com/fleetdm/fleet/v4 Versions

1 component(s)
Fixed Versions:
4.81.0
Product / Package Ecosystem Affected Versions Fixed Version
github.com/fleetdm/fleet/v4
golang/github.com/fleetdm/fleet/v4
Go
< 4.81.0
4.81.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fleetdm/fleet/security/advisories/GHSA-w254-4hp5-7cvv
NVD — CVE-2026-34388 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-34388
Github.com/fleetdm/fleet/v4 Source Repository REPOSITORY
https://github.com/fleetdm/fleet

Frequently Asked Questions

What is CVE-2026-34388?
CVE-2026-34388 is a security vulnerability in Github.com/fleetdm/fleet/v4 involving Fleet vulnerable to Denial of Service via unhandled gRPC log type in launcher endpoint under CWE-703: Improper Check or Handling of Exceptional Conditions.
Which Github.com/fleetdm/fleet/v4 versions are affected?
Affected versions include releases prior to 4.81.0 across affected packages: github.com/fleetdm/fleet/v4.
What version fixes CVE-2026-34388?
Upgrading to 4.81.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/fleetdm/fleet/v4 affected?
Yes, github.com/fleetdm/fleet/v4 is affected in releases prior to 4.81.0. Upgrade your dependency to 4.81.0 or later.
What CWE is associated with CVE-2026-34388?
CVE-2026-34388 is classified under CWE-703: Improper Check or Handling of Exceptional Conditions (The product does not properly anticipate or handle exceptional conditions that rarely occur during normal operation of the product.).
How can I check Go dependencies for CVE-2026-34388?
Run the dependency tree command: 'inspect dependencies for github.com/fleetdm/fleet/v4'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-w254-4hp5-7cvv",
  "modified" : "2026-03-30T19:22:39Z",
  "published" : "2026-03-30T19:22:39Z",
  "aliases" : [ "CVE-2026-34388" ],
  "summary" : "Fleet vulnerable to Denial of Service via unhandled gRPC log type in launcher endpoint",
  "details" : "### Summary\n\nA 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.\n\n### Impact\n\nAn 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.\n\nBecause 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.\n\n### Workarounds\n\nThere is no workaround for this issue other than upgrading to a patched version.\n\n### For more information\n\nIf there are any questions or comments about this advisory:\n\nSend an email to  [security@fleetdm.com](mailto:security@fleetdm.com)\n\nJoin #fleet in [osquery Slack](https://join.slack.com/t/osquery/shared_invite/zt-h29zm0gk-s2DBtGUTW4CFel0f0IjTEw)\n\n### Credits\n\nFleet thanks @fuzzztf for responsibly reporting this issue.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fleetdm/fleet/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.81.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fleetdm/fleet/security/advisories/GHSA-w254-4hp5-7cvv"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-34388"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fleetdm/fleet"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-703" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-30T19:22:39Z",
    "nvd_published_at" : "2026-03-27T20:16:35Z"
  }
}