RouterOS does not compare the complete RSA public key when validating an SSH authentication request, checking only the key type and modulus while omitting the exponent. Because signature verification uses the key supplied by the client, an attacker who knows the authorized RSA modulus can supply a key with an exponent of one, forge a valid signature, and obtain an SSH session as the target user without needing the private key. This capability allows an attacker to gain SSH access as the impersonated account, thereby enabling execution of arbitrary commands with that account’s privileges.

The vulnerability affects Mikrotik RouterOS 7.x releases older than 7.23.4 (Long-term) and 7.24.2 (Stable). Any device running these older releases is susceptible if RSA key authentication is enabled for any user.

With a CVSS score of 9.2 the vulnerability is considered critical. The EPSS score is 6%, indicating a higher probability of exploitation, yet reports of active exploitation exist in the wild. The attack vector is remote, requiring an attacker to establish an SSH session and supply a forged key.