# CVE-2018-1000874: Cross-site scripting in n/a

> A maliciously crafted markdown payload can execute arbitrary scripts in the context of the user viewing the parsed content, potentially leading to data theft.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A: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:** 20 Dec 2018
- **Updated:** 6 May 2025
- **Also known as:** GHSA-gvg5-fmh4-q8jg

## What is CVE-2018-1000874?

CVE-2018-1000874 is a medium-severity cross-site scripting vulnerability in n/a, published on 20 Dec 2018. 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

PHP cebe markdown parser version 1.2.0 and earlier contains a Cross Site Scripting (XSS) vulnerability in all distributed parsers allowing a malicious crafted script to be executed that can result in the lose of user data and sensitive user information. This attack can be exploited by crafting a three backtick wrapped payload with a character in front: L: "```<script>alert();</script>```". NOTE: This has been argued as a non-issue (see references) since it is not the parser's job to sanitize malicious code from a parsed document

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2018-1000874?

It affects 1 product.


Products: Cebe Markdown.

## How do I fix CVE-2018-1000874?

No fix has been published for CVE-2018-1000874 yet. Limit exposure of the affected software until one is available.

## Is CVE-2018-1000874 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2018-1000874 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2018-1000874 and fix it if it is affected.

What it is: CVE-2018-1000874 is a medium-severity cross-site scripting vulnerability in n/a, published on 20 Dec 2018. 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-2018-1000874 exists.

Affected product: n/a. 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-2018-1000874/ (Markdown: https://insights.sbomify.com/CVE-2018-1000874/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2018-1000874
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2018-1000874
- OSV: https://osv.dev/vulnerability/CVE-2018-1000874

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From sbomify Insights: https://insights.sbomify.com/CVE-2018-1000874/
Summaries are generated and may contain mistakes; the official description above is the record.