CVE-2026-39042Network attack vector

Pre-authentication service crash via wrapped message length

Published Jul 13, 2026 · Updated Jul 13, 2026

Integer overflow in MikroTik RouterOS 7.21.x before 7.21.4 and 7.22.x before 7.22.2 allows remote attackers to crash services. The LONG-string handler in nv::message::unflatten() adds an attacker-controlled 32-bit length to the current buffer position without overflow checking, letting the end pointer wrap past its bounds test and drive an approximately 4 GB allocation. Pre-authentication reachability through default management services lets crafted messages crash the affected service, which the RouterOS watchdog then restarts.

CVSS severity7.5
High
EPSS probability0.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Integer overflow in MikroTik RouterOS 7.21.x before 7.21.4 and 7.22.x before 7.22.2 allows remote attackers to crash services. The LONG-string handler in nv::message::unflatten() adds an attacker-controlled 32-bit length to the current buffer position without overflow checking, letting the end pointer wrap past its bounds test and drive an approximately 4 GB allocation. Pre-authentication reachability through default management services lets crafted messages crash the affected service, which the RouterOS watchdog then restarts.

The record

CVE
CVE-2026-39042
Published
Jul 13, 2026
Updated
Jul 13, 2026
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-190, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 13, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-190Integer Overflow or Wraparound
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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