# CVE-2026-84411: MikroTik RouterOS Integer Underflow

> Unauthenticated attackers can achieve root code execution or cause denial of service via integer underflow in RouterOS web management.

- **Severity:** Critical 9.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 2 Oct 2026
- **Updated:** 3 Oct 2026
- **Also known as:** GHSA-xj4h-hf2x-2q43

## What is CVE-2026-84411?

CVE-2026-84411 is a critical vulnerability in MikroTik RouterOS, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

The web management service in affected RouterOS versions contains an integer underflow in its HTTP request body handling that is reachable before authentication. This can be leveraged by an unauthenticated network attacker to achieve arbitrary code execution as root, or to cause a denial of service, using a single crafted request.

Weakness: CWE-191 (Integer Underflow (Wrap or Wraparound))

## Which versions are affected by CVE-2026-84411?


## How do I fix CVE-2026-84411?

No fix has been published for CVE-2026-84411 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-84411 being exploited?

There is no known exploitation of CVE-2026-84411 in the wild and no public exploit code.

Public exploit code:

- CVE-2026-84411 root cause notes and a non-destructive probe (RouterOS before 7.24) (github_poc): https://github.com/Apiratchai/CVE-2026-84411-reproduction
-  CVE-2026-84411 — MikroTik RouterOS WebFig Integer Underflow Exploit (github_poc): https://github.com/maxprog-svg/CVE-2026-84411

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-84411 and fix it if it is affected.

What it is: CVE-2026-84411 is a critical vulnerability in MikroTik RouterOS, published on 2 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-84411 in the wild and no public exploit code.

Affected product: MikroTik RouterOS. 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-2026-84411/ (Markdown: https://insights.sbomify.com/CVE-2026-84411/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-84411
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-84411
- OSV: https://osv.dev/vulnerability/CVE-2026-84411

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-84411/
Summaries are generated and may contain mistakes; the official description above is the record.