CVE-2026-89020: MikroTik RouterOS Stack Buffer Overflow via TFTP URL Path

Vulnerability summary

CVE-2026-89020 is a medium (CVSS 5.3) Stack-based Buffer Overflow vulnerability in mikrotik routeros. EPSS estimates a 0.49% chance of exploitation in the next 30 days, higher than 41% of scored vulnerabilities.

Timeline

1. 14-09-2026
   PublishedVulnerability first disclosed.
2. 01-10-2026
   Last modifiedVulnerability information updated.

Description

MikroTik RouterOS before 7.23.4 (long-term) and 7.24.2 (stable) contains a stack-based buffer overflow vulnerability in the mtget binary's TFTP RRQ builder function that allows authenticated users to crash the mtget worker process by supplying a URL path of 507 bytes or more to the /tool fetch command; the first write outside the 528-byte buffer occurs at 505 bytes. Attackers can trigger the overflow by issuing a fetch command with a crafted tftp:// URL path, which causes an unbounded rep movsb instruction to overwrite saved registers at a deterministic offset, crashing the process without requiring a reachable TFTP server or elevated privileges beyond read-only group membership.

• CWE-121Stack-based Buffer OverflowA stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).