# CVE-2020-15164: Authentication Bypass in Scratch Login (mediawiki-scratch-login)

> Attackers can bypass authentication and take over any account by manipulating underscores in usernames due to improper input handling in the Scratch Login extension.

- **Severity:** Critical 10.0 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/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:** 28 Aug 2020
- **Updated:** 4 Aug 2024

## What is CVE-2020-15164?

CVE-2020-15164 is a critical authentication bypass vulnerability in InternationalScratchWiki mediawiki-scratch-login, published on 28 Aug 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

in Scratch Login (MediaWiki extension) before version 1.1, any account can be logged into by using the same username with leading, trailing, or repeated underscore(s), since those are treated as whitespace and trimmed by MediaWiki. This affects all users on any wiki using this extension. Since version 1.1, comments by users whose usernames would be trimmed on MediaWiki are ignored when searching for the verification code.

Weakness: CWE-74 (Improper Neutralization of Special Elements in Output Used by a Downstream Component), CWE-287 (Improper Authentication)

## Which versions are affected by CVE-2020-15164?

It affects 1 product.


Products: Scratch-Wiki Scratch Login.

## How do I fix CVE-2020-15164?

No fix has been published for CVE-2020-15164 yet. Limit exposure of the affected software until one is available.

## Is CVE-2020-15164 being exploited?

There is no known exploitation of CVE-2020-15164 in the wild and no public exploit code.

## Other vulnerabilities in InternationalScratchWiki mediawiki-scratch-login

- [CVE-2022-42985](https://insights.sbomify.com/CVE-2022-42985/): Cross-site scripting in n/a (medium 4.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-15164 and fix it if it is affected.

What it is: CVE-2020-15164 is a critical authentication bypass vulnerability in InternationalScratchWiki mediawiki-scratch-login, published on 28 Aug 2020. 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-2020-15164 in the wild and no public exploit code.

Affected product: InternationalScratchWiki mediawiki-scratch-login. 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-2020-15164/ (Markdown: https://insights.sbomify.com/CVE-2020-15164/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-15164
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-15164
- OSV: https://osv.dev/vulnerability/CVE-2020-15164

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-15164/
Summaries are generated and may contain mistakes; the official description above is the record.