# CVE-2026-55210: Joplin: SAML SSO account takeover via email-based account linking (missing is_external check in ssoLogin)

> Attackers can take over local Joplin accounts via SAML SSO by exploiting missing external account checks in mixed authentication deployments.

- **Severity:** High 7.4 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 21 Sep 2026
- **Updated:** 22 Sep 2026
- **Also known as:** GHSA-5px3-4f5x-hjc5

## What is CVE-2026-55210?

CVE-2026-55210 is a high-severity authentication bypass vulnerability in laurent22 joplin, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Joplin is an open source note-taking and to-do application that organises notes and lists into notebooks. Prior to 3.7.2, Joplin Server's UserModel.ssoLogin() returns an existing account matched by an IdP-asserted email without checking the account's is_external flag. In deployments using mixed local and SAML authentication, an attacker whose IdP session can assert a local user's email can pass POST /api/saml, receive a session for that local account, and access or modify the victim's notes, files, and settings without knowing the local password. This issue is fixed in version 3.7.2.

Weakness: CWE-290 (Authentication Bypass by Spoofing)

## Which versions are affected by CVE-2026-55210?


## How do I fix CVE-2026-55210?

No fix has been published for CVE-2026-55210 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-55210 being exploited?

There is no known exploitation of CVE-2026-55210 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-55210 and fix it if it is affected.

What it is: CVE-2026-55210 is a high-severity authentication bypass vulnerability in laurent22 joplin, published on 21 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-55210 in the wild and no public exploit code.

Affected product: laurent22 joplin. 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-2026-55210/ (Markdown: https://insights.sbomify.com/CVE-2026-55210/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-55210
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-55210
- OSV: https://osv.dev/vulnerability/CVE-2026-55210

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-55210/
Summaries are generated and may contain mistakes; the official description above is the record.