CVE-2026-81036

What it is

Stalwart Mail Server does not compare an OAuth redirect target against any registered destination in its default configuration. The validation routine in crates/http/src/auth/oauth/registration.rs returns success immediately when the client-authentication requirement is disabled, and that requirement is false in the shipped settings, so the supplied redirect value is neither matched against a registered client nor otherwise constrained. The value is stored with the authorization code, and the login page reads it back and sends the browser to it with the code attached. A request naming a destination the attacker controls therefore delivers a valid authorization code there once the account holder authenticates, and because the token endpoint checks only that the redirect presented at exchange matches the one recorded with the code, the same party can exchange it for access and refresh tokens and read the account's mail.

At a glance

Exploitability

Can be exploited over the network without logging in, but needs a user to act. High risk of data exposure, data tampering.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

1. 2026-08-26 16:16 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-09-24 20:43 UTC Last updatedMost recent change to the record

Details

Published

2026-08-26 16:16 UTC

Last modified

2026-09-24 20:43 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-601

Record status

Deferred

Attack profile CVSS 4.0 · 8.5

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

Active

Confidentiality

High

Integrity

High

Availability

None