CVE-2026-18678: Kumactl Information Disclosure Flaw

CVE-2026-18678 Overview

CVE-2026-18678 affects kumactl, the command-line interface for the Kuma service mesh control plane. When an operator adds an HTTPS control plane profile without providing a certificate authority (CA) certificate, kumactl silently disables TLS verification. The client then transmits API tokens over the unverified connection.

An attacker positioned on the network path between the operator and the control plane can intercept user or administrator API tokens. The attacker can then reuse those tokens to act against the control plane with the victim's privileges. The weakness is classified as [CWE-295: Improper Certificate Validation].

Critical Impact
Adjacent-network attackers can intercept administrator API tokens and impersonate legitimate operators against the Kuma control plane.

Affected Products

Kuma service mesh kumactl command-line interface
Kong Mesh (built on Kuma) kumactl client
Deployments where HTTPS control plane profiles are configured without an explicit CA certificate

Discovery Timeline

2026-08-12 - CVE-2026-18678 published to the National Vulnerability Database (NVD)
2026-08-12 - Last updated in NVD database

Technical Details for CVE-2026-18678

Vulnerability Analysis

The kumactl utility manages control plane profiles that hold connection details, including the control plane URL and authentication material. When an operator configures an HTTPS profile, the client should validate the server certificate against a trusted CA before sending credentials.

Instead, kumactl falls back to a permissive mode when no CA certificate is supplied. TLS verification is disabled entirely, meaning the client accepts any certificate presented by the endpoint at the configured URL. Once the profile is used, kumactl attaches the stored API token to requests and sends them over the unauthenticated TLS channel.

Because the token grants access at the same privilege level as the operator, capture of an administrator token yields full control plane access. The flaw is a classic insecure default: HTTPS provides the appearance of security while omitting the certificate check that gives TLS its guarantees.

Root Cause

The root cause is improper certificate validation [CWE-295] in the kumactl profile handling logic. Absence of a user-supplied CA certificate is treated as an instruction to skip verification, rather than as a configuration error. The fix is tracked in GitHub Pull Request #16777 and documented in GitHub Security Advisory GHSA-v95x-xhq5-4929.

Attack Vector

An attacker must occupy a position on the network path between the operator's workstation and the Kuma control plane, such as a shared LAN, a compromised gateway, or a rogue Wi-Fi network. The attacker presents a substitute TLS certificate for the control plane hostname. Because kumactl does not verify the certificate, the client completes the handshake and transmits the API token. The attacker then replays the token against the legitimate control plane API to enumerate resources, modify mesh policies, or issue administrative operations.

No synthetic exploitation code is included. Refer to GitHub Security Advisory GHSA-v95x-xhq5-4929 for maintainer-provided technical details.

Detection Methods for CVE-2026-18678

Indicators of Compromise

Unexpected TLS certificates presented for the Kuma control plane hostname, particularly certificates signed by an unrecognized issuer.
API activity from source IP addresses that do not match the operator's known workstations or jump hosts.
Control plane audit log entries showing policy changes, token creation, or user actions outside normal operator working hours.

Detection Strategies

Inspect kumactl configuration files under the operator's home directory for HTTPS profile entries that omit a caCert field.
Enable and centralize Kuma control plane audit logs, then correlate administrative API calls against approved operator sessions.
Deploy TLS inspection or certificate transparency monitoring on the network segments used to reach the control plane.

Monitoring Recommendations

Alert on new or rotated certificates presented by the control plane endpoint that were not issued by the organization's internal CA.
Track API token usage patterns and flag reuse from geographies or hosts inconsistent with the token owner.
Monitor for concurrent kumactl sessions authenticating with the same token from different network locations.

How to Mitigate CVE-2026-18678

Immediate Actions Required

Upgrade kumactl to a fixed release of Kuma or Kong Mesh as identified in GitHub Security Advisory GHSA-v95x-xhq5-4929 and the Kong Mesh Changelog.
Rotate all user and administrator API tokens that may have been used through an HTTPS profile lacking a CA certificate.
Audit existing kumactl profiles and remove or reconfigure any HTTPS entry without an explicit CA certificate.

Patch Information

The upstream fix is delivered through GitHub Pull Request #16777 in the kumahq/kuma repository. Kong Mesh distributions integrate the fix through their corresponding release; consult the Kong Mesh Changelog for the specific version that addresses CVE-2026-18678.

Workarounds

Always supply a CA certificate when adding an HTTPS control plane profile so that kumactl performs full certificate validation.
Restrict control plane access to trusted network paths, for example via a VPN or bastion host, until the client is upgraded.
Use short-lived API tokens with least-privilege scopes to limit the window and impact of token interception.

bash

# Configuration example: add a kumactl control plane profile with an explicit CA certificate
kumactl config control-planes add \
  --name=production \
  --address=https://kuma-cp.example.internal:5682 \
  --ca-cert-file=/etc/pki/ca-trust/source/anchors/internal-ca.pem \
  --auth-type=tokens \
  --auth-conf token=$(cat ~/.kuma/tokens/admin.token)