# CVE-2025-35435: CISA Thorium download stream divide by zero

> A remote authenticated attacker can crash the CISA Thorium service by providing a zero stream split size, causing a divide-by-zero error.

- **Severity:** Medium 5.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/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:** 17 Sep 2025
- **Updated:** 30 Sep 2025
- **Also known as:** GHSA-w2x7-fc9j-4572

## What is CVE-2025-35435?

CVE-2025-35435 is a medium-severity denial of service vulnerability in CISA Thorium, published on 17 Sep 2025. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

CISA Thorium accepts a stream split size of zero then divides by this value. A remote, authenticated attacker could cause the service to crash. Fixed in commit 89101a6.

Weakness: CWE-369 (Divide By Zero)

## Which versions are affected by CVE-2025-35435?

It affects 1 product.


Products: Cisa Thorium.

## How do I fix CVE-2025-35435?

No fix has been published for CVE-2025-35435 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-35435 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-35435 exists.

## Other vulnerabilities in CISA Thorium

- [CVE-2025-35432](https://insights.sbomify.com/CVE-2025-35432/): CISA Thorium does not rate limit account verification email messages (medium 6.9)
- [CVE-2025-35436](https://insights.sbomify.com/CVE-2025-35436/): CISA Thorium account verification email error handling (medium 6.9)
- [CVE-2025-35430](https://insights.sbomify.com/CVE-2025-35430/): CISA Thorium insecure downloaded file path validation (medium 5.3)
- [CVE-2025-35431](https://insights.sbomify.com/CVE-2025-35431/): CISA Thorium LDAP injection (medium 5.3)
- [CVE-2025-35433](https://insights.sbomify.com/CVE-2025-35433/): CISA Thorium does not properly invalidate previously used tokens (low 2.3)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-35435 and fix it if it is affected.

What it is: CVE-2025-35435 is a medium-severity denial of service vulnerability in CISA Thorium, published on 17 Sep 2025. 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-2025-35435 exists.

Affected product: CISA Thorium. 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-2025-35435/ (Markdown: https://insights.sbomify.com/CVE-2025-35435/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-35435
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-35435
- OSV: https://osv.dev/vulnerability/CVE-2025-35435

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-35435/
Summaries are generated and may contain mistakes; the official description above is the record.