CVE-2026-81036 Stalwart Mail Server through 0.16.19 Authorization Code Disclosure via Unvalidated OAuth redirect_uri
Attackers can steal OAuth authorization codes via unvalidated redirect URIs to take over user accounts and read mail.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-81036?
CVE-2026-81036 is a high-severity vulnerability in stalwartlabs stalwart, published on 26 Aug 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-601
Which versions are affected by CVE-2026-81036?
How do I fix CVE-2026-81036?
No fix has been published for CVE-2026-81036 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-81036 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-81036 exists.
Sources
Also known as GHSA-g6qf-h8rr-h574.