# CVE-2026-103903: MikroTik RouterOS WinBox split-principal authentication bypass allows privilege escalation

> Low-privilege WinBox users can bypass authentication checks to gain full administrative privileges on MikroTik RouterOS devices.

- **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:** 12 Oct 2026
- **Updated:** 13 Oct 2026
- **Also known as:** GHSA-23wm-v672-9cvc

## What is CVE-2026-103903?

CVE-2026-103903 is a high-severity authentication bypass vulnerability in MikroTik RouterOS, published on 12 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

An incorrect authorization vulnerability in the WinBox
authentication flow of MikroTik RouterOS allows a remote authenticated attacker
with credentials for a low-privilege account permitted to use WinBox to obtain
the authorization policy of a different existing account. The stage-one EC-SRP
challenge and proof are verified using the attacker's account, while the
independently supplied stage-two username is used to install the target
account's privileges. By specifying a higher-privilege account such as admin, a
low-privilege user can obtain a full administrative session without knowing the
target account's password and can use that session to increase the privileges
of the attacker's own account.

Weakness: CWE-863 (Incorrect Authorization)

## Which versions are affected by CVE-2026-103903?


## How do I fix CVE-2026-103903?

No fix has been published for CVE-2026-103903 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103903 being exploited?

There is no known exploitation of CVE-2026-103903 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103903 and fix it if it is affected.

What it is: CVE-2026-103903 is a high-severity authentication bypass vulnerability in MikroTik RouterOS, published on 12 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-103903 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-2026-103903/ (Markdown: https://insights.sbomify.com/CVE-2026-103903/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103903
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103903
- OSV: https://osv.dev/vulnerability/CVE-2026-103903

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103903/
Summaries are generated and may contain mistakes; the official description above is the record.