# CVE-2026-121862: Knowledge Building < 0.7.3 - Unauthenticated Stored XSS via knbu_new_reply AJAX Action

> Unauthenticated users can store scripts in Knowledge Building replies that run for any visitor, including administrators.

- **Severity:** High 8.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H`)
- **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
- **Harmful if only installed:** No
- **Needs a specific call:** No
- **Fix available:** No
- **Published:** 11 Nov 2026
- **Updated:** 11 Nov 2026
- **Also known as:** GHSA-vxm8-8rj5-3798

## What is CVE-2026-121862?

CVE-2026-121862 is a high-severity cross-site scripting vulnerability in Unknown Knowledge Building, published on 11 Nov 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

The Knowledge Building WordPress plugin before 0.7.3 does not sanitise and escape comments submitted through its reply feature, and publishes them without moderation, allowing unauthenticated users to perform Stored Cross-Site Scripting attacks against any visitor of the affected posts, including administrators.

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

## Which versions are affected by CVE-2026-121862?

An affected version is exposed as installed. No special setting or call is needed.


## How do I fix CVE-2026-121862?

No fix has been published for CVE-2026-121862 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-121862 being exploited?

There is no known exploitation of CVE-2026-121862 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-121862 and fix it if it is affected.

What it is: CVE-2026-121862 is a high-severity cross-site scripting vulnerability in Unknown Knowledge Building, published on 11 Nov 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: There is no known exploitation of CVE-2026-121862 in the wild and no public exploit code.
Exposure: An affected version is exposed as installed. No special setting or call is needed.

Affected product: Unknown Knowledge Building. 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-2026-121862/ (Markdown: https://insights.sbomify.com/CVE-2026-121862/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-121862
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121862
- OSV: https://osv.dev/vulnerability/CVE-2026-121862

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-121862/
Summaries are generated and may contain mistakes; the official description above is the record.