CVE-2026-26062: Github.com/fleetdm/fleet/v4 Fleet Server May Terminate Unexpectedly Vulnerability

HIGH
Advisory Identifier: GHSA-x67p-9m2r-fxqv
Share
CWE-20
Published
Advisory Summary

CVE-2026-26062 is a HIGH fleet server may terminate unexpectedly vulnerability (CWE-20: Improper Input Validation) affecting Github.com/fleetdm/fleet/v4 libraries in the Go ecosystem. The issue involves fleet server may terminate unexpectedly when handling certain grpc requests. Remediation is available by upgrading affected packages to version 4.81.0.

CVE-2026-26062 at a Glance

CVE Identifier CVE-2026-26062
GHSA Identifier GHSA-x67p-9m2r-fxqv
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-20: Improper Input Validation
Affected Product Github.com/fleetdm/fleet/v4
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-26062

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-2026-26062, 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-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. 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 Fleet contained a denial-of-service (DoS) issue in the gRPC Launcher `PublishLogs` endpoint. In affected versions, certain unexpected input values were not handled gracefully, which could cause the Fleet server process to terminate while processing an authenticated request from an enrolled Launcher host. ### Impact An authenticated attacker with access to any enrolled Launcher node key could cause an immediate and complete denial of service by sending a single gRPC request to the `PublishLogs` endpoint. This vulnerability impacts **availability only**. There is: - No exposure of sensitive data - No authentication bypass - No privilege escalation - No integrity impact ### Workarounds If upgrading immediately is not possible, the following mitigations can reduce exposure: - Restrict network access to the Fleet gRPC endpoint where feasible (for example, limiting inbound access to known host IP ranges). - Deploy Fleet behind infrastructure that terminates or filters gRPC traffic if Launcher log ingestion is not required. - Monitor for repeated Fleet process crashes or unexpected restarts indicating potential exploitation. ### For More Information If you have any questions or concerns about this advisory, please contact us at: Email us at [security@fleetdm.com](mailto:security@fleetdm.com) ### Credits We thank @fuzzztf for responsibly reporting this issue.

CVE-2026-26062 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-x67p-9m2r-fxqv
NVD — CVE-2026-26062 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-26062
Github.com/fleetdm/fleet/v4 Source Repository REPOSITORY
https://github.com/fleetdm/fleet
Github.com/fleetdm/fleet/v4 Release RELEASE
https://github.com/fleetdm/fleet/releases/tag/fleet-v4.81.0

Frequently Asked Questions

What is CVE-2026-26062?
CVE-2026-26062 is a security vulnerability in Github.com/fleetdm/fleet/v4 involving Fleet server may terminate unexpectedly when handling certain gRPC requests under CWE-20: Improper Input Validation.
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-2026-26062?
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-2026-26062?
CVE-2026-26062 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check Go dependencies for CVE-2026-26062?
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-x67p-9m2r-fxqv",
  "modified" : "2026-05-15T23:45:30Z",
  "published" : "2026-05-14T13:17:18Z",
  "aliases" : [ "CVE-2026-26062" ],
  "summary" : "Fleet server may terminate unexpectedly when handling certain gRPC requests",
  "details" : "### Summary\n\nFleet contained a denial-of-service (DoS) issue in the gRPC Launcher `PublishLogs` endpoint. In affected versions, certain unexpected input values were not handled gracefully, which could cause the Fleet server process to terminate while processing an authenticated request from an enrolled Launcher host.\n\n### Impact\n\nAn authenticated attacker with access to any enrolled Launcher node key could cause an immediate and complete denial of service by sending a single gRPC request to the `PublishLogs` endpoint.\n\nThis vulnerability impacts **availability only**. There is:\n\n- No exposure of sensitive data\n- No authentication bypass\n- No privilege escalation\n- No integrity impact\n\n### Workarounds\n\nIf upgrading immediately is not possible, the following mitigations can reduce exposure:\n\n- Restrict network access to the Fleet gRPC endpoint where feasible (for example, limiting inbound access to known host IP ranges).\n- Deploy Fleet behind infrastructure that terminates or filters gRPC traffic if Launcher log ingestion is not required.\n- Monitor for repeated Fleet process crashes or unexpected restarts indicating potential exploitation.\n\n### For More Information\n\nIf you have any questions or concerns about this advisory, please contact us at:\n\nEmail us at [security@fleetdm.com](mailto:security@fleetdm.com)\n\n### Credits\n\nWe thank @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"
  } ],
  "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-x67p-9m2r-fxqv"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26062"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fleetdm/fleet"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/fleetdm/fleet/releases/tag/fleet-v4.81.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-05-14T13:17:18Z",
    "nvd_published_at" : "2026-05-14T20:17:02Z"
  }
}