CVE-2026-93345 in MikroTik
Summary
by MITRE • 09/22/2026
MikroTik RouterOS before 7.25beta4 contains an improper input validation vulnerability in the labelled-VPN NLRI iterators of the routing service that allows an unauthenticated on-path attacker to crash the BGP service by sending a malformed MP_REACH_NLRI UPDATE message with a prefix-length value below the minimum valid for a labelled-VPN NLRI, which passes validation while describing a route with a negative-length address portion. Attackers can repeatedly send a single BGP UPDATE packet carrying a VPNv4 or VPNv6 NLRI with an out-of-bounds prefix-length to indefinitely hold down the BGP plane, causing session termination without a NOTIFICATION and triggering a service malfunction on the device.
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Analysis
by VulDB Data Team • 09/22/2026
The vulnerability identified in MikroTik RouterOS versions prior to 7.25beta4 represents a critical flaw within the Border Gateway Protocol implementation, specifically targeting the processing of Multiprotocol Reachability Information NLRI iterators used for labelled-VPN routes. This improper input validation issue allows an unauthenticated attacker positioned on-path to disrupt network operations by exploiting how the routing service parses UPDATE messages. The core technical failure lies in the insufficient verification of prefix-length values associated with VPNv4 and VPNv6 Network Layer Reachability Information fields. When a BGP peer sends an MP_REACH_NLRI UPDATE message containing a prefix-length that is below the minimum valid threshold for labelled-VPN NLRI, the system fails to reject this malformed data immediately. Instead, it proceeds to process the route description which effectively describes an address portion with negative length due to arithmetic underflow or logical misinterpretation of the bit boundaries.
This processing error leads directly to a denial-of-service condition by crashing or hanging the BGP service plane on the affected device. The operational impact is severe as the vulnerability enables indefinite hold-downs of the BGP state machine without triggering standard session termination notifications such as NOTIFICATION messages with appropriate error codes. Consequently, the routing process becomes unresponsive, preventing the router from exchanging route updates and effectively isolating it within its autonomous system or network segment. An attacker can exploit this by repeatedly sending a single crafted BGP UPDATE packet carrying these malformed NLRI structures, ensuring that any attempt to recover the session is thwarted because the service remains in a malfunctioning state rather than gracefully closing the connection.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation and CWE-190 Integer Overflow or Wraparound if the negative length results from arithmetic errors during bit calculation. In terms of offensive security frameworks, it maps to MITRE ATT&CK technique T1498 Network Denial of Service, specifically sub-technique T1498.002 Resource Exhaustion via Floods, as the attacker aims to exhaust service resources or logic paths rather than bandwidth alone. The lack of authentication requirement for this exploit makes it particularly dangerous in environments where BGP peers are not strictly authenticated using MD5 signatures or TCP-AO, although even with authentication, an on-path attacker who has compromised credentials could leverage this flaw.
Mitigation strategies primarily involve upgrading to MikroTik RouterOS version 7.25beta4 or later where the input validation logic for labelled-VPN NLRI iterators has been corrected to properly reject prefix-length values that fall outside valid ranges before processing begins. In environments where immediate patching is not feasible, network administrators should implement strict access control lists on BGP peer interfaces to restrict source IP addresses to only known and trusted peers. Additionally, deploying intrusion prevention systems capable of deep packet inspection for BGP protocol anomalies can help detect and block malformed UPDATE messages containing invalid NLRI structures before they reach the routing engine. Regular monitoring of BGP session stability logs is also recommended to identify potential exploitation attempts characterized by sudden service hangs or unexpected peer state changes without standard teardown notifications.