# CVE-2026-9520: blitz-js blitz Sign-in LoginForm.tsx cross site scripting

> Cross-site scripting in Blitz.js sign-in form allows remote attackers to inject scripts, potentially leading to session hijacking or code execution.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA: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:** 26 May 2026
- **Updated:** 27 May 2026
- **Also known as:** GHSA-h2p9-cr4h-px24

## What is CVE-2026-9520?

CVE-2026-9520 is a medium-severity cross-site scripting vulnerability in blitz-js blitz, published on 26 May 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

A weakness has been identified in blitz-js blitz up to 3.0.2 on GitHub. This impacts an unknown function of the file packages/generator/templates/app/src/app/auth/components/LoginForm.tsx of the component Sign-in. This manipulation of the argument Next causes cross site scripting. It is possible to initiate the attack remotely. The exploit has been made available to the public and could be used for attacks. The vendor was contacted early about this disclosure but did not respond in any way.

Weakness: CWE-94 (Improper Control of Generation of Code), CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2026-9520?

2 open source packages ship an affected version, including blitz.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `blitz` | npm | All versions to 3.0.2 | None |
| `blitz` | npm | All versions to 3.0.2 | None |

## How do I fix CVE-2026-9520?

No fix has been published for CVE-2026-9520 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-9520 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-9520 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-9520 and fix it if it is affected.

What it is: CVE-2026-9520 is a medium-severity cross-site scripting vulnerability in blitz-js blitz, published on 26 May 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: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-9520 exists.

Affected packages and fixed versions:
- blitz (npm): affected all versions up to 3.0.2; no fix listed
- blitz (npm): affected all versions up to 3.0.2; 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-2026-9520/ (Markdown: https://insights.sbomify.com/CVE-2026-9520/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-9520
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-9520
- OSV: https://osv.dev/vulnerability/CVE-2026-9520

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-9520/
Summaries are generated and may contain mistakes; the official description above is the record.