# CVE-2026-103974: lichess.org: Stored HTML Injection via PGN Annotator Tag in Studies

> Attackers can inject stored HTML and CSS into chess studies, enabling content spoofing and data exposure for other viewers.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 14 Oct 2026
- **Updated:** 14 Oct 2026
- **Also known as:** GHSA-43g7-r6hp-ccf8

## What is CVE-2026-103974?

CVE-2026-103974 is a medium-severity cross-site scripting vulnerability in lichess-org lila, published on 14 Oct 2026. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

### Official description

lichess.org is the forever free, adless and open source chess server. Prior to commit c54596c9e1569d378fe20f80d4c790c6fdee54c4, a user who can add a chapter to a study can place attacker-controlled text in the PGN Annotator tag, which becomes Comment.Author.External and is returned verbatim by authorText. When a study node has at least two comments, ui/analyse/src/treeView/inlineView.ts interpolates that author string into HTML passed to the innerHTML hook without escaping it. Opening the affected study can therefore render stored attacker-controlled HTML and CSS for other viewers, including navigation to an attacker-controlled site, content spoofing, and CSS-based data exposure, although the site's content security policy blocks injected JavaScript. This vulnerability is fixed by commit c54596c9e1569d378fe20f80d4c790c6fdee54c4.

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

## Which versions are affected by CVE-2026-103974?


## How do I fix CVE-2026-103974?

No fix has been published for CVE-2026-103974 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103974 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-103974 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103974 and fix it if it is affected.

What it is: CVE-2026-103974 is a medium-severity cross-site scripting vulnerability in lichess-org lila, published on 14 Oct 2026. Any signed-in user can exploit it over the network, 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-2026-103974 exists.

Affected product: lichess-org lila. 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-2026-103974/ (Markdown: https://insights.sbomify.com/CVE-2026-103974/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103974
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103974
- OSV: https://osv.dev/vulnerability/CVE-2026-103974

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103974/
Summaries are generated and may contain mistakes; the official description above is the record.