CVE-2026-26061: Github.com/fleetdm/fleet/v4 Denial of Service Vulnerability

HIGH
Advisory Identifier: GHSA-99hj-44vg-hfcp
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CWE-770
Published
Advisory Summary

CVE-2026-26061 is a HIGH denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Github.com/fleetdm/fleet/v4 libraries in the Go ecosystem. The issue involves fleet's unbounded request body read allows remote denial of service. Remediation is available by upgrading affected packages to version 4.43.5-0.20260113202849-bbc1aef2987d.

CVE-2026-26061 at a Glance

CVE Identifier CVE-2026-26061
GHSA Identifier GHSA-99hj-44vg-hfcp
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Github.com/fleetdm/fleet/v4
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-26061

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: 4.43.5-0.20260113202849-bbc1aef2987d 
Upgrade github.com/fleetdm/fleet/v4 to 4.43.5-0.20260113202849-bbc1aef2987d
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-2026-26061, 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 4.43.5-0.20260113202849-bbc1aef2987d), 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-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. 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 multiple unauthenticated HTTP endpoints that read request bodies without enforcing a size limit. An unauthenticated attacker could exploit this behavior by sending large or repeated HTTP payloads, causing excessive memory allocation and resulting in a denial-of-service (DoS) condition. ### Impact An unauthenticated attacker could cause the Fleet server process to exhaust available memory and restart by sending oversized or repeated HTTP requests to affected endpoints. 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: - Apply request body size limits at a reverse proxy or load balancer (e.g., NGINX, Envoy). - Restrict network access to endpoints to known IP ranges where feasible. - Monitor memory usage and restart frequency for abnormal patterns. ### For More Information If there are any questions or concerns about this advisory, please contact us at: Email Fleet at [security@fleetdm.com](mailto:security@fleetdm.com) ### Credits Fleet thanks @fuzzztf for responsibly reporting this issue.

CVE-2026-26061 Affected Github.com/fleetdm/fleet/v4 Versions

1 component(s)
Fixed Versions:
4.43.5-0.20260113202849-bbc1aef2987d
Product / Package Ecosystem Affected Versions Fixed Version
github.com/fleetdm/fleet/v4
golang/github.com/fleetdm/fleet/v4
Go
< 4.43.5-0.20260113202849-bbc1aef2987d
4.43.5-0.20260113202849-bbc1aef2987d

References

GitHub Advisory / Wiki ADVISORY
https://github.com/fleetdm/fleet/security/advisories/GHSA-99hj-44vg-hfcp
NVD — CVE-2026-26061 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-26061
Github.com/fleetdm/fleet/v4 Source Repository REPOSITORY
https://github.com/fleetdm/fleet

Frequently Asked Questions

What is CVE-2026-26061?
CVE-2026-26061 is a security vulnerability in Github.com/fleetdm/fleet/v4 involving Fleet's unbounded request body read allows remote Denial of Service under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Github.com/fleetdm/fleet/v4 versions are affected?
Affected versions include releases prior to 4.43.5-0.20260113202849-bbc1aef2987d across affected packages: github.com/fleetdm/fleet/v4.
What version fixes CVE-2026-26061?
Upgrading to 4.43.5-0.20260113202849-bbc1aef2987d (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 4.43.5-0.20260113202849-bbc1aef2987d. Upgrade your dependency to 4.43.5-0.20260113202849-bbc1aef2987d or later.
What CWE is associated with CVE-2026-26061?
CVE-2026-26061 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check Go dependencies for CVE-2026-26061?
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-99hj-44vg-hfcp",
  "modified" : "2026-03-27T21:47:50Z",
  "published" : "2026-03-27T18:17:42Z",
  "aliases" : [ "CVE-2026-26061" ],
  "summary" : "Fleet's unbounded request body read allows remote Denial of Service",
  "details" : "### Summary\n\nFleet contained multiple unauthenticated HTTP endpoints that read request bodies without enforcing a size limit. An unauthenticated attacker could exploit this behavior by sending large or repeated HTTP payloads, causing excessive memory allocation and resulting in a denial-of-service (DoS) condition.\n\n### Impact\n\nAn unauthenticated attacker could cause the Fleet server process to exhaust available memory and restart by sending oversized or repeated HTTP requests to affected endpoints.\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- Apply request body size limits at a reverse proxy or load balancer (e.g., NGINX, Envoy).\n- Restrict network access to endpoints to known IP ranges where feasible.\n- Monitor memory usage and restart frequency for abnormal patterns.\n\n### For More Information\n\nIf there are any questions or concerns about this advisory, please contact us at:\n\nEmail Fleet at [security@fleetdm.com](mailto:security@fleetdm.com)\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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/fleetdm/fleet/v4"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "4.43.5-0.20260113202849-bbc1aef2987d"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/fleetdm/fleet/security/advisories/GHSA-99hj-44vg-hfcp"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-26061"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/fleetdm/fleet"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-770" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-27T18:17:42Z",
    "nvd_published_at" : "2026-03-27T19:16:42Z"
  }
}