# CVE-2026-40521: FrontAccounting < 2.4.20 Path Traversal RCE via attachment upload

> Authenticated attackers can achieve remote code execution by uploading malicious files via path traversal in the attachment handler.

- **Severity:** High 8.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 29 Jun 2026
- **Updated:** 14 Jul 2026
- **Also known as:** GHSA-9fmm-h59x-wr53

## What is CVE-2026-40521?

CVE-2026-40521 is a high-severity path traversal vulnerability in FrontAccounting, published on 29 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

FrontAccounting before 2.4.20 contains a path traversal vulnerability in the attachment upload handler that allows authenticated attackers to execute arbitrary code by uploading files with traversal sequences in the unique_name parameter. Attackers can supply path traversal sequences ../../../shell.php to write files outside the intended attachments directory into the web root, and by uploading PHP files without extension validation, achieve remote code execution as the web server user.

Weakness: CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-40521?


## How do I fix CVE-2026-40521?

No fix has been published for CVE-2026-40521 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-40521 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40521 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40521 and fix it if it is affected.

What it is: CVE-2026-40521 is a high-severity path traversal vulnerability in FrontAccounting, published on 29 Jun 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40521 exists.

Affected product: FrontAccounting. 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-2026-40521/ (Markdown: https://insights.sbomify.com/CVE-2026-40521/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40521
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40521
- OSV: https://osv.dev/vulnerability/CVE-2026-40521

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40521/
Summaries are generated and may contain mistakes; the official description above is the record.