# 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.

- **Severity:** High 8.5 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **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 available:** No
- **Published:** 26 Aug 2026
- **Updated:** 29 Aug 2026
- **Also known as:** GHSA-g6qf-h8rr-h574

## 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 (URL Redirection to Untrusted Site)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-81036 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-81036 exists.

Affected product: stalwartlabs stalwart. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-81036/ (Markdown: https://insights.sbomify.com/CVE-2026-81036/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-81036
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-81036
- OSV: https://osv.dev/vulnerability/CVE-2026-81036

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-81036/
Summaries are generated and may contain mistakes; the official description above is the record.