# CVE-2026-23873: HUSTOJ is Vulnerable to Stored CSV Injection (Formula Injection) in Contest Rank Export

> Attackers can execute arbitrary commands or exfiltrate data on an administrator's machine by injecting Excel formulas into user nicknames exported to CSV.

- **Severity:** Medium 5.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:N/VI:N/VA:N/SC:H/SI:H/SA:H`)
- **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:** 21 Jan 2026
- **Updated:** 22 Jan 2026
- **Also known as:** GHSA-gqwv-v7vx-2qjw

## What is CVE-2026-23873?

CVE-2026-23873 is a medium-severity code injection vulnerability in zhblue hustoj, published on 21 Jan 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

hustoj is an open source online judge based on PHP/C++/MySQL/Linux for ACM/ICPC and NOIP training. All versions are vulnerable to CSV Injection (Formula Injection) through the contest rank export functionality (contestrank.xls.php and admin/ranklist_export.php). The application fails to sanitize user-supplied input (specifically the "Nickname" field) before exporting it to an .xls file (which renders as an HTML table but is opened by Excel). If a malicious user sets their nickname to an Excel formula when an administrator exports and opens the rank list in Microsoft Excel, the formula will be executed. This can lead to arbitrary command execution (RCE) on the administrator's machine or data exfiltration. A fix was not available at the time of publication.

Weakness: CWE-1236 (Improper Neutralization of Formula Elements in a CSV File)

## Which versions are affected by CVE-2026-23873?

It affects 1 product.


Products: Hustoj Hustoj.

## How do I fix CVE-2026-23873?

No fix has been published for CVE-2026-23873 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-23873 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-23873 exists.

## Other vulnerabilities in zhblue hustoj

- [CVE-2026-24479](https://insights.sbomify.com/CVE-2026-24479/): HUSTOJ has Arbitrary File Write (Zip Slip) in Problem Import Modules that leads to RCE (critical 9.3)
- [CVE-2025-50938](https://insights.sbomify.com/CVE-2025-50938/): Cross-site scripting in n/a (medium 6.1)
- [CVE-2022-42187](https://insights.sbomify.com/CVE-2022-42187/): Cross-site scripting in n/a (medium 6.1)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-23873 and fix it if it is affected.

What it is: CVE-2026-23873 is a medium-severity code injection vulnerability in zhblue hustoj, published on 21 Jan 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-2026-23873 exists.

Affected product: zhblue hustoj. 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-2026-23873/ (Markdown: https://insights.sbomify.com/CVE-2026-23873/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-23873
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-23873
- OSV: https://osv.dev/vulnerability/CVE-2026-23873

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-23873/
Summaries are generated and may contain mistakes; the official description above is the record.