Executive brief
MikroTik RouterOS, which manages network routing and connectivity, contains a flaw in its SSH authentication system that allows attackers to log in without the legitimate user's private key. An attacker who knows a user's public key modulus can craft a counterfeit key and gain remote command execution with the victim's privileges. This vulnerability is actively being exploited to compromise routers exposed to the internet.
Technical details
The SSH server fails to validate the complete RSA public key during authentication, comparing only the key type and modulus while omitting verification of the exponent. An attacker supplies a key with exponent one, which produces valid signatures using the client-supplied key, bypassing authentication. Exploitation requires network access to SSH and knowledge of an authorized user's RSA modulus; no user interaction is needed.
Affected products
- MikroTik RouterOS 7.x branch; fixed in 7.23.4 (Long-term) and 7.24.2 (Stable)
Timeline
- 2026-09-05: disclosed
- 2026-09-05: exploited: actively exploited in the wild targeting internet-exposed devices