Listen to this Post
How CVE-2026-41053 Works
A vulnerability has been identified within Rancher Manager in the GitHub App authentication provider. When evaluating permissions, the provider incorrectly expands user team memberships to include all teams within the associated GitHub organization, rather than restricting access to the specific teams to which the user actually belongs.
Specifically, when a user authenticates via the GitHub App provider, Rancher’s team membership evaluation logic incorrectly handles cached data. Instead of checking the user-specific list, the evaluation logic iterates over all teams defined within the entire GitHub organization. The authentication provider should consult the correctly cached, per-user membership list to assign the user’s specific group permissions. Consequently, any authenticated user who belongs to at least one team in a GitHub organization is mistakenly granted group principals for every team within that entire organization during authentication and authorization checks.
This issue allows a malicious user who is a member of a low-privilege team within a GitHub organization to gain unauthorized access to or permissions for any other team in that organization. If those other teams are bound to Rancher login allowlists or RBAC roles (cluster-level, project-level, or global), the attacker can pass access checks that should otherwise fail, inheriting permissions they were never granted.
Exploitation of this vulnerability requires the following conditions to be met:
– The GitHub App authentication provider must be enabled and configured for the target GitHub organization.
– The attacker must possess a valid GitHub account with membership in at least one team within that target organization.
– A separate team within the same GitHub organization must be explicitly mapped to Rancher RBAC roles or specified within Rancher’s login allowlist (allowedPrincipalIds).
This vulnerability is classified as CWE-303: Incorrect Implementation of Authentication Algorithm and maps to CAPEC-233: Privilege Escalation. The CVSS v3.1 score is 8.8 (HIGH) with the vector CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H.
DailyCVE Form
Platform: Rancher Manager
Version: 2.13.0–2.13.5, 2.14.0–2.14.1
Vulnerability: Over-inclusive team membership expansion
Severity: HIGH (CVSS 8.8)
Date: 2026-05-28
Prediction: 2026-05-28 (Patched)
What Undercode Say
“Incorrect authentication caching in the team membership expansion of the Rancher Github authentication provider caused it granting principal access to any logged in user.”
Analytics & Technical Details:
- Root Cause: The evaluation logic iterates over all teams defined within the entire GitHub organization instead of consulting the per-user membership cache.
- Fix: The team listing logic now iterates only the teams stored in the per-user membership cache, with a one-time startup migration marking all affected User resources for refresh.
- Patched Versions: v2.14.2 and v2.13.6.
Bash Commands & Codes:
Check current Rancher version
kubectl get deployment rancher -n cattle-system -o jsonpath='{.spec.template.spec.containers[bash].image}'
Upgrade to patched version (Helm)
helm upgrade rancher rancher-stable/rancher \
--namespace cattle-system \
--set hostname=rancher.example.com \
--version 2.14.2
Verify upgrade
kubectl rollout status deployment rancher -n cattle-system
Audit RBAC Bindings for GitHub App Teams:
List all ClusterRoleBindings referencing GitHub teams
kubectl get clusterrolebindings -o json | jq '.items[] | select(.subjects[]?.kind=="Group" and .subjects[]?.name | contains("github_org"))'
List all GlobalRoleBindings
kubectl get globalrolebindings -o yaml
Exploit
- Attacker authenticates to Rancher via the GitHub App provider with a GitHub account that belongs to at least one team in the target organization.
- Rancher’s flawed caching logic grants the attacker group principals for every team within the entire GitHub organization.
- The attacker leverages these inflated group principals to bypass RBAC checks, gaining unauthorized access to cluster-level, project-level, or global permissions bound to any team in the organization.
Protection
- Immediate: Upgrade to Rancher v2.14.2 or v2.13.6.
- Workarounds (if upgrade is not feasible):
- Disable the GitHub App authentication provider and switch to GitHub OAuth.
- Remove or restrict team-based group principals from
allowedPrincipalIds. - Audit and temporarily remove RBAC bindings (
GlobalRoleBindings,ClusterRoleTemplateBindings,ProjectRoleTemplateBindings) that reference GitHub App team principals. - Disable provider refresh and clean up inflated group memberships manually or via script.
Impact
- Unauthorized Access: Any authenticated user belonging to at least one team in a GitHub organization can inherit permissions from all teams in that organization.
- Privilege Escalation: A low-privilege user can gain cluster-admin or project-owner permissions if those roles are bound to any team in the organization.
- Security Controls Bypass: Login allowlists and RBAC checks are rendered ineffective, allowing attackers to pass access checks that should otherwise fail.
References:
🎯Let’s Practice Exploiting & Learn Patching For Free:
🎓 Live Courses & Certifications:
Join Undercode Academy for Verified Certifications
🚀 Request a Custom Project:
Secure, high-velocity infrastructure and disruptive technological engineering. Contact our engineering team for high-tier development and proprietary systems:
[email protected]
💎 Smart Architecture | 🛡️ Secure by Design | ⭐ Trusted by Thousands
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
