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.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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
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.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-103903 being exploited?
There is no known exploitation of CVE-2026-103903 in the wild and no public exploit code.
Sources
Also known as GHSA-23wm-v672-9cvc.