CVE-2026-39388: OpenBao's Certificate Authentication Allows Token Renewal With Different Certificate
Background
OpenBao's Certificate authentication method, when a token renewal is requested and disablebinding=true is set, attempts to verify the current request's presented mTLS certificate matches the original. Token renewals for other authentication methods do not require any supplied login information.
Impact
Due to incorrect matching, the certificate authentication method would allow renewal of tokens for which the attacker had a sibling certificate+key signed by the same CA, but which did not necessarily match the original role or the originally supplied certificate. This implies an attacker could still authenticate to OpenBao in a similar scope, however, token renewal implies that an attacker may be able to extend the lifetime of dynamic leases held by the original token. This attack requires knowledge of either the original token or its accessor.
This vulnerability is originally from HashiCorp Vault.
Patches
This has been addressed in v2.5.3.
Workarounds
Ensure privileged roles are tightly scoped to single certificates.
Other sources
OpenBao is an open source identity-based secrets management system. Prior to version 2.5.3, OpenBao's Certificate authentication method, when a token renewal is requested and disablebinding=true is set, attempts to verify the current request's presented mTLS certificate matches the original. Token renewals for other authentication methods do not require any supplied login information. Due to incorrect matching, the certificate authentication method would allow renewal of tokens for which the attacker had a sibling certificate+key signed by the same CA, but which did not necessarily match the original role or the originally supplied certificate. This implies an attacker could still authenticate to OpenBao in a similar scope, however, token renewal implies that an attacker may be able to extend the lifetime of dynamic leases held by the original token. This attack requires knowledge of either the original token or its accessor. This vulnerability is original from HashiCorp Vault. This is addressed in v2.5.3. As a workaround, ensure privileged roles are tightly scoped to single certificates.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2026-39388?
CVE-2026-39388 has been classified as a high-severity vulnerability due to its potential impact on the security of token renewals.
How do I fix CVE-2026-39388?
To mitigate CVE-2026-39388, upgrade OpenBao to version 2.5.3 or later.
What are the potential impacts of CVE-2026-39388?
CVE-2026-39388 could allow unauthorized token renewal through different certificates, compromising the system's authentication.
What versions of OpenBao are affected by CVE-2026-39388?
CVE-2026-39388 affects all versions of OpenBao prior to 2.5.3.
Is there a workaround for CVE-2026-39388?
A temporary workaround involves disabling certificate authentication or ensuring `disable_binding` is not set to true until an update can be applied.