CISA warns of critical pre-auth RCE flaw in MikroTik RouterOS

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) is warning of a new critical vulnerability in MikroTik RouterOS that could lead to remote code execution or cause a denial-of-service condition.

Tracked as CVE-2026-84411, the security issue is a pre-authentication integer underflow in RouterOS’s web-management HTTP request handling.

CISA says that a single crafted request can produce code execution with root privileges or denial of service.

“The web management service in affected RouterOS versions contains an integer underflow in its HTTP request body handling that is reachable before authentication,” reads the alert.

“This can be leveraged by an unauthenticated network attacker to achieve arbitrary code execution as root, or to cause a denial of service, using a single crafted request.”

Although the agency has no knowledge of the vulnerability being actively exploited, it released the advisory to alert organizations of the risk and to provide defensive measures.

CISA notes that MikroTik RouterOS versions below 7.24 are currently affected. However, the agency also says that the vendor recommends that users update to version 7.23 or later to mitigate the risk.

It should be noted that the latest stable version of MikroTik RouterOS is 7.24.4, while the most recent long-term release is 7.23.7, both available since September 16.

BleepingComputer has emailed both MikroTik and CISA for clarification about the RouterOS versions affected by CVE-2026-84411, but we have not received a response as of publication. The vendor has yet to publish a security advisory about the issue.

CISA's recommendations to MikroTik router owners include the following defensive actions:

1. Keep control systems inaccessible from the internet.
2. Place control networks and remote devices behind firewalls, isolated from business networks.
3. Use updated VPNs for remote access and secure all connected devices.

Although no active exploitation of CVE-2026-84411 has been publicly disclosed, hackers and botnet malware often target MikroTik flaws.

Recently, Poland’s CERT agency warned that attackers used an exploit chain of two MikroTik RouterOS vulnerabilities, CVE-2026-67276 and CVE-2026-86060, to take full control of devices with SSH services exposed to the internet.

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