# CVE-2023-26131: Algernon engine and themes vulnerable to Cross-site Scripting

> An attacker can execute arbitrary scripts in a victim's browser via improper input sanitization in the Algernon Go web framework when a resource is missing.

- **Severity:** Medium 5.4 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N/E:P`)
- **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:** 31 May 2023
- **Updated:** 9 Jan 2025
- **Also known as:** GHSA-g47h-fgcw-g4ph

## What is CVE-2023-26131?

CVE-2023-26131 is a medium-severity cross-site scripting vulnerability in github.com/xyproto/algernon/engine, published on 31 May 2023. 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

All versions of the package github.com/xyproto/algernon/engine; all versions of the package github.com/xyproto/algernon/themes are vulnerable to Cross-site Scripting (XSS) via the themes.NoPage(filename, theme) function due to improper user input sanitization. Exploiting this vulnerability is possible when a file/resource is not found.

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

## Which versions are affected by CVE-2023-26131?

2 open source packages ship an affected version, including github.com/xyproto/algernon. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/xyproto/algernon` | Go | All versions to 1.15.2 | None |
| `github.com/xyproto/algernon` | Go | All versions to 1.15.2 | None |

Products: Algernon Project Algernon.

## How do I fix CVE-2023-26131?

No fix has been published for CVE-2023-26131 yet. Limit exposure of the affected software until one is available.

## Is CVE-2023-26131 being exploited?

There is no known exploitation of CVE-2023-26131 in the wild and no public exploit code.

## Other vulnerabilities in github.com/xyproto/algernon/engine

- [CVE-2025-65754](https://insights.sbomify.com/CVE-2025-65754/): Algernon Cross-Site Scripting vulnerability (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2023-26131 and fix it if it is affected.

What it is: CVE-2023-26131 is a medium-severity cross-site scripting vulnerability in github.com/xyproto/algernon/engine, published on 31 May 2023. 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-2023-26131 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/xyproto/algernon (Go): affected all versions up to 1.15.2; no fix listed
- github.com/xyproto/algernon (Go): affected all versions up to 1.15.2; no fix listed

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-2023-26131/ (Markdown: https://insights.sbomify.com/CVE-2023-26131/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-26131
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-26131
- OSV: https://osv.dev/vulnerability/CVE-2023-26131

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-26131/
Summaries are generated and may contain mistakes; the official description above is the record.