EUVD-2026-67680
GHSA-856w-5q8f-fq73
Severity by source
AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Network-accessible auth bypass; AC:H reflects dual preconditions (absent scope claim plus audience/scope name collision); PR:N because no prior authentication to Dovecot is required; no availability impact from token acceptance.
Primary rating from Vendor (OX).
CVSS VectorVendor: OX
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
Lifecycle Timeline
3DescriptionCVE.org
An attacker that holds a token intended for a different purpose can authenticate, because when an OAuth2 token response does not contain a scope claim, the audience claim is used in its place and checked against the configured required scopes. These are different concepts, and the audience claim does not describe what a token is allowed to do. A token that grants no relevant permissions can be accepted because its intended recipient value happens to match a configured scope name, granting access that should have been denied. It also hides an identity provider misconfiguration where scopes are not being issued at all. Ensure the identity provider issues a scope claim for all tokens used with Dovecot, and that configured scope names do not match audience values. Update to non-vulnerable version. No publicly available exploits are known.
AnalysisAI
OAuth2 token validation in OX Dovecot Pro and OX Dovecot CE contains a logic error that permits authentication bypass when the identity provider omits the scope claim from token responses. Dovecot incorrectly falls back to evaluating the audience claim as a substitute for scope, accepting any token whose audience value coincidentally matches a configured scope name - regardless of what permissions that token actually grants. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Two concurrent conditions must be satisfied: (1) the OAuth2 identity provider must issue tokens that omit the scope claim - either due to IDP misconfiguration or because the grant type in use does not enforce scope issuance - and (2) the audience (aud) value in the attacker's token must match at least one scope name configured in Dovecot's OAuth2 settings. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS vector AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N captures a network-exploitable authentication bypass with high attack complexity driven by two concurrent prerequisites: the IDP must omit the scope claim, and the token's audience value must coincidentally match a Dovecot-configured scope name. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | The primary remediation is to upgrade to the non-vulnerable version of OX Dovecot Pro or OX Dovecot CE as specified in the Open-Xchange advisory at https://documentation.open-xchange.com/dovecot/security/advisories/csaf/2026/oxdc-adv-2026-0003.json - exact fixed version numbers must be confirmed from that advisory, as they are not available in current intelligence data. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory all OX Dovecot Pro and CE instances configured with OAuth2 authentication and contact your identity provider to confirm that scope claims are included in all token responses; simultaneously enable detailed authentication and token validation logging on all affected Dovecot servers to establish a baseline for anomaly detection. …
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External POC / Exploit Code
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