MikroTik 'MikroTrick' SSH bypass chain hijacks internet-exposed routers; CISA adds two flaws to KEV with September 13 deadline

MikroTik RouterOS 7.x fails to compare the complete RSA public key when matching an SSH authentication attempt against an authorized user key, checking the key type and modulus but omitting the exponent. Because RouterOS verifies the signature against the client-supplied key, an attacker who knows the modulus of an authorized RSA key can present a key with exponent 1 and a forged signature and be accepted as that user without possessing the private key. Successful exploitation opens an SSH command channel as the target user, giving the attacker control of the router without a password or key. Only the RouterOS 7.x branch is affected, with fixes released in 7.23.4 (Long-term) and 7.24.2 (Stable). A public proof-of-concept is available and related reporting describes active campaigns hijacking MikroTik routers using chained RouterOS flaws, though this CVE is not in CISA KEV and its 30-day EPSS probability is low (0.2%).

Do: Upgrade affected devices to RouterOS 7.23.4 (Long-term) or 7.24.2 (Stable) or later. Until patched, restrict SSH access to trusted management networks and, if feasible, remove or replace RSA authorized keys with other key types. Check devices for signs of compromise highlighted in recent reporting, such as an unexpected SSH user named '-2'.

CVE-2026-86060 is an argument-injection flaw (CWE-88) in MikroTik RouterOS's SSH login path: when a login supplies a username beginning with a prohibited character, the RouterOS login helper mishandles the argument, allowing the trusted RouterOS policy mask to be changed and privileges to be escalated. An unauthenticated attacker only needs the ability to reach the router's SSH service, since exploitation happens during the SSH login process itself. By altering the policy mask the attacker gains elevated rights on the device, and news reports indicate attackers have used this technique — including logins with usernames such as '-2' — as part of chains that take over routers without needing a password. Any RouterOS deployment running versions before the fixes (6.49.21 Long-term, 7.23.4 Long-term, 7.24.2 Stable) with SSH enabled or reachable is affected, with internet-exposed SSH at highest risk. Multiple outlets report the RouterOS flaws are being actively exploited in the wild, although no public proof-of-concept is known and the flaw is not yet in CISA KEV.

Do: Upgrade RouterOS to 6.49.21 (Long-term), 7.23.4 (Long-term) or 7.24.2 (Stable) as applicable. Until patched, restrict SSH (TCP 22) to trusted management networks or disable the SSH service if unused, and review authentication logs and user/group policy settings for tampering — reports indicate attackers log in with usernames beginning with '-' (e.g., '-2').

MikroTik RouterOS 7.x improperly verifies RSA/PKCS#1 v1.5 signatures when validating X.509 certificate chains, accepting malformed signatures (CWE-347, Improper Verification of Cryptographic Signature). Because the RouterOS trust store includes a root CA whose public key uses the small exponent e=3, an attacker who can control or redirect one of the router's outbound TLS connections (for example via a network man-in-the-middle position, DNS hijacking, or a compromised upstream path) can forge an intermediate CA signed with the root's public key, without ever holding its private key, and mint trusted certificates for arbitrary hostnames. This lets the attacker impersonate TLS servers the router connects to, with low confidentiality and integrity impact per the CVSS 4.0 score of 6.3 (medium), which reflects the network vector, no privileges required, but a high attack requirement of holding such a network position. Any deployment running RouterOS 7.x before 7.23.4 (Long-term) or 7.24.2 (Stable) is affected, spanning home/SOHO, enterprise, and ISP/WISP infrastructure; the 6.x branch is not listed as affected. No public proof-of-concept is known, the issue is not in CISA's KEV, and EPSS gives a 0.2% probability of exploitation within 30 days, although related headlines note other MikroTik flaws have recently been chained to hack routers.

Do: Upgrade RouterOS 7.x to 7.23.4 (Long-term track) or 7.24.2 (Stable track). Until patched, reduce the chance an attacker can sit on the router's outbound TLS path by hardening DNS resolvers, avoiding untrusted upstream networks, and restricting management-plane exposure, since exploitation requires controlling or redirecting an outbound connection. Given other RouterOS flaws have recently been chained in router hijacks, prioritize patching internet-exposed and ISP/WISP infrastructure devices.

CVE-2026-67279 is an authentication-ordering flaw (CWE-841) in the SSH server of MikroTik RouterOS: after a client-requested SSH rekey, the server enters the connection protocol even though user authentication was never attempted. An unauthenticated SSH client can therefore open a session channel and send an exec request, and on affected builds the server dispatches the command without any credentials. This lets the attacker create, overwrite, and reconstruct files in the RouterOS managed file namespace, including support files that contain configuration and diagnostic data. Any MikroTik device running RouterOS builds older than the fixed releases is affected, although remote exploitation requires the SSH service to be reachable by the attacker. No public proof-of-concept is known, the issue is not in CISA's KEV catalog, and EPSS estimates a 0.4% probability of exploitation in the next 30 days, so no exploitation is currently known.

Do: Upgrade RouterOS to 6.49.21 (Long-term v6), 7.23.4 (Long-term v7), or 7.24.2 (Stable). Until patched, restrict SSH access to trusted management networks/VPN or disable the SSH service where it is not needed. Review the RouterOS file list and SSH logs for unexpected or reconstructed files and session activity, since attackers have recently chained multiple MikroTik flaws against routers.

RouterOS WebFig's /jsproxy handler contains an unauthenticated file-read flaw: a newly allocated session keeps a stale, uninitialized principal pointer that is later used to authorize file access (CWE-824), combined with a path-traversal issue (CWE-22). An unauthenticated attacker who can reach the web interface first shapes the heap allocator so the uninitialized pointer resolves with sufficient rights, then submits an encrypted URI containing parent-directory components to escape the WebFig file namespace. This lets the attacker read root-owned files on the router, including configuration stores that contain credentials, which could enable further compromise. Only MikroTik RouterOS 7.x before 7.23.4 (Long-term) and 7.24.2 (Stable) is affected. No public proof-of-concept, KEV listing, or confirmed in-the-wild exploitation of this flaw is known (EPSS ~0.4%), although recent reporting notes MikroTik patches being chained in router-hijack campaigns generally.

Do: Upgrade affected routers to RouterOS 7.23.4 (Long-term) or 7.24.2 (Stable). Until patched, restrict the www/WebFig service (and /jsproxy) to trusted management networks or VPN access and firewall WAN access to the router's web interface. Check logs for unauthenticated requests to /jsproxy containing traversal patterns, and rotate credentials found in router configuration stores if unexplained access is observed.