CVE-2026-102508: Apache PLC4X: OPC UA secure channel: integrity bypass, unverifiable server certificate, and silent downgrade
Improper Verification of Cryptographic Signature and Improper Certificate Validation in the OPC UA driver of Apache PLC4X (PLC4J) allows an attacker in a network position between client and server to impersonate the OPC UA server and to read, forge or modify secure-channel traffic, including user credential ssent by the client.
The defect manifests differently depending on the version: - In 0.9.0 through 0.11.0 a failed message-signature check is only logged and never enforced, and there is no mechanism to verify the server certificate: it is taken from the unauthenticated GetEndpoints discovery response and used to encrypt the user's password. - In 0.12.0 through 0.13.1 the signature check is inverted (valid signatures are rejected, invalid ones accepted), and server certificates are accepted without a trust anchor by default. - In all affected versions the default security policy is None. Starting with 0.12.0 the driver additionally continues silently at a weaker security policy than the one configured, and starting with 0.13.0 endpoint selection prefers the weakest matching endpoint.
Users checking only for one of these mechanisms may wrongly conclude they are unaffected.
This issue affects Apache PLC4X: from 0.9.0 before 1.0.0.
Users are recommended to upgrade to version 1.0.0, which fixes the issue. Version 1.0.0 verifies message signatures correctly, refuses to connect unless the server certificate can be verified against a configured trust store or pinned certificate, defaults to Basic256Sha256 with SignAndEncrypt, and fails the connection if the negotiated security policy is weaker than the configured one.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Apache PLC4X (PLC4J) OPC UA driverto a version that resolves this vulnerability.Fixed in 1.0.0
Event History
Frequently Asked Questions
Who can exploit this issue?
An attacker must be in a network position between the PLC4X OPC UA client and server. From that position, they can impersonate the server and read, forge, or modify secure-channel traffic, including credentials sent by the client.
Are deployments using default settings affected?
Yes. The default security policy is None in all affected versions. In 0.12.0 through 0.13.1, server certificates are also accepted without a trust anchor by default; 0.12.0 and later can silently continue with weaker security than configured.
How does exposure differ by PLC4J version?
Versions 0.9.0 through 0.11.0 log failed message-signature checks without enforcing them and cannot verify the server certificate. Versions 0.12.0 through 0.13.1 reject valid signatures while accepting invalid ones; from 0.13.0, endpoint selection also prefers the weakest matching endpoint.