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

Severity: medium (CVSS 4.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-14 · updated 2026-09-24
Weakness: CWE-121

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.

Affected products

MikroTik RouterOS: before 7.23.4; from 7.24.0 before 7.24.2 — fixed in 7.23.4, 7.24.2

How to fix

Upgrade to a fixed version: MikroTik RouterOS 7.23.4, 7.24.2. Check the vendor advisory for mitigations.

References

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