Service interruption via reused receive timeout
Published Jul 13, 2026 · Updated Jul 13, 2026
Denial of service in libmodbus 3.1.12 on Windows allows remote attackers to block Modbus TCP request handling with slow byte delivery. The modbus_receive loop reuses the full indication timeout after each partial read because Windows select() does not decrement the timeval structure as the loop assumes. A reachable single-threaded server with byte timeout disabled remains unavailable to normal clients until the slow connection closes.
Summary
What happened
Denial of service in libmodbus 3.1.12 on Windows allows remote attackers to block Modbus TCP request handling with slow byte delivery. The modbus_receive loop reuses the full indication timeout after each partial read because Windows select() does not decrement the timeval structure as the loop assumes. A reachable single-threaded server with byte timeout disabled remains unavailable to normal clients until the slow connection closes.
The record
- CVE
- CVE-2026-51539
- Published
- Jul 13, 2026
- Updated
- Jul 13, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-400, T1499.003
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 13, 2026CVE publishedPublication date reported by the CVE source.
- 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?
What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
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.
Weakness, pattern, technique
Public exploit references
- Slowloris-style libmodbus Windows proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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