Medium [CVE-2026-40205] Authorization bypass via partially valid OAuth2 token
This medium-severity Red Hat Linux advisory covers CVE-2026-40205 affecting Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7.
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Summary
An attacker that holds an OAuth2 token granting only part of the required scopes can authenticate, because when more than one scope is required in the configuration, the remote token validation paths accept a token that carries only one of them, while the local token validation path correctly requires all of them.
The configured authorization policy is not enforced, so a token that was granted only part of the required permissions is accepted where it should have been rejected. Use local token validation where tokens can be validated locally.
Update to non-vulnerable version. No publicly available exploits are known.
A flaw was found in Dovecot. This allows the attacker to authenticate with insufficient permissions, leading to a breach of integrity where the configured authorization policy is not properly enforced.
Red Hat severity: Moderate — CVSS 5.9 (CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N). Weakness: CWE-303.
Affected Red Hat products: Red Hat Enterprise Linux 10; Red Hat Enterprise Linux 6; Red Hat Enterprise Linux 7; Red Hat Enterprise Linux 8; Red Hat Enterprise Linux 9. Will not fix / out of support: Red Hat Enterprise Linux 6.
Red Hat does not currently list a fixing RHSA for this CVE.
Affected products named by the advisory: Red Hat package: dovecot.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Fixed versions
No fixed release is recorded yet. That does not prove no patch exists — confirm against the vendor advisory.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- To mitigate this issue, configure Dovecot to use local OAuth2 token validation instead of remote validation. This ensures that all required scopes are correctly enforced during authentication, preventing unauthorized access with partially valid tokens. Consult Dovecot documentation for specific configuration steps to enable local token validation. A service restart may be required for the changes to take effect.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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