CVE-2021-20609

Uncontrolled Resource Consumption vulnerability in Mitsubishi Electric MELSEC iQ-R Series R00/01/02CPU, MELSEC iQ-R Series R04/08/16/32/120(EN)CPU, MELSEC iQ-R Series R08/16/32/120SFCPU, MELSEC iQ-R Series R08/16/32/120PCPU, MELSEC iQ-R Series R08/16/32/120PSFCPU, MELSEC iQ-R Series R16/32/64MTCPU, MELSEC iQ-R Series R12CCPU-V, MELSEC Q Series Q03UDECPU, MELSEC Q Series Q04/06/10/13/20/26/50/100UDEHCPU, MELSEC Q Series Q03/04/06/13/26UDVCPU, MELSEC Q Series Q04/06/13/26UDPVCPU, MELSEC Q Series Q12DCCPU-V, MELSEC Q Series Q24DHCCPU-V(G), MELSEC Q Series Q24/26DHCCPU-LS, MELSEC Q Series MR-MQ100, MELSEC Q Series Q172/173DCPU-S1, MELSEC Q Series Q172/173DSCPU, MELSEC Q Series Q170MCPU, MELSEC Q Series Q170MSCPU(-S1), MELSEC L Series L02/06/26CPU(-P), MELSEC L Series L26CPU-(P)BT and MELIPC Series MI5122-VW allows a remote unauthenticated attacker to cause a denial-of-service (DoS) condition by sending specially crafted packets. System reset is required for recovery.

Published: 2021-12-01 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-20609 is rated Moderate Risk (62.8/100): CVSS High severity, with medium exploitation likelihood (EPSS 3.08%). EPSS rose +2.74% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-20609

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.34% 3.08% +2.74%
2 2026-02-14 0.48% 0.34% -0.14%
3 2025-12-08 — 0.48% —

Full EPSS history (18 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20609

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.8 2.0 HIGH
AV:N/AC:L/Au:N/C:N/I:N/A:C Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:C)
Complete availability impact.
 10.0 6.9 [email protected]

Weakness enumeration for CVE-2021-20609

Affected software / configurations for CVE-2021-20609

Vendor Product Version Raw CPE
mitsubishi melsec_iq-r_r00_cpu_firmware <= 24 cpe:2.3:o:mitsubishi:melsec_iq-r_r00_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r01_cpu_firmware <= 24 cpe:2.3:o:mitsubishi:melsec_iq-r_r01_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r02_cpu_firmware <= 24 cpe:2.3:o:mitsubishi:melsec_iq-r_r02_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r04_cpu_firmware <= 57 cpe:2.3:o:mitsubishi:melsec_iq-r_r04_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r08_cpu_firmware <= 57 cpe:2.3:o:mitsubishi:melsec_iq-r_r08_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r120_cpu_firmware <= 57 cpe:2.3:o:mitsubishi:melsec_iq-r_r120_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r16_cpu_firmware <= 57 cpe:2.3:o:mitsubishi:melsec_iq-r_r16_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r32_cpu_firmware <= 57 cpe:2.3:o:mitsubishi:melsec_iq-r_r32_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r04_pcpu_firmware <= 29 cpe:2.3:o:mitsubishi:melsec_iq-r_r04_pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r08_pcpu_firmware <= 29 cpe:2.3:o:mitsubishi:melsec_iq-r_r08_pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r16_pcpu_firmware <= 29 cpe:2.3:o:mitsubishi:melsec_iq-r_r16_pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r32_pcpu_firmware <= 29 cpe:2.3:o:mitsubishi:melsec_iq-r_r32_pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r120_pcpu_firmware <= 29 cpe:2.3:o:mitsubishi:melsec_iq-r_r120_pcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r08_sfcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r08_sfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r16_sfcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r16_sfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r32_sfcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r32_sfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r120_sfcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r120_sfcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r16_mtcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r16_mtcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r32_mtcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r32_mtcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r64_mtcpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r64_mtcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r12_ccpu-v_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r12_ccpu-v_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q03udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q03udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q04udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q04udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q06udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q06udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q10udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q10udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q13udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q13udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q20udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q20udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q26udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q26udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q50udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q50udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q100udecpu_firmware — cpe:2.3:o:mitsubishi:melsec_q100udecpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q03udvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q03udvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q04udvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q04udvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q06udvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q06udvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q13udvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q13udvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q26udvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q26udvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q04udpvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q04udpvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q06udpvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q06udpvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q13udpvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q13udpvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q26udpvcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q26udpvcpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q12dccpu-v_firmware — cpe:2.3:o:mitsubishi:melsec_q12dccpu-v_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q24dhccpu-v\(g\)_firmware — cpe:2.3:o:mitsubishi:melsec_q24dhccpu-v\(g\)_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q24dhccpu-ls_firmware — cpe:2.3:o:mitsubishi:melsec_q24dhccpu-ls_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q26dhccpu-ls_firmware — cpe:2.3:o:mitsubishi:melsec_q26dhccpu-ls_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_mr-mq100_firmware — cpe:2.3:o:mitsubishi:melsec_mr-mq100_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q172dcpu-s1_firmware — cpe:2.3:o:mitsubishi:melsec_q172dcpu-s1_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q173dcpu-s1_firmware — cpe:2.3:o:mitsubishi:melsec_q173dcpu-s1_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q172dscpu_firmware — cpe:2.3:o:mitsubishi:melsec_q172dscpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q173dscpu_firmware — cpe:2.3:o:mitsubishi:melsec_q173dscpu_firmware:-:*:*:*:*:*:*:*
mitsubishi melsec_q170mscpu\(-s1\)_firmware — cpe:2.3:o:mitsubishi:melsec_q170mscpu\(-s1\)_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_q170mcpu_firmware — cpe:2.3:o:mitsubishi:melsec_q170mcpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melipc_mi5122-vw_firmware — cpe:2.3:o:mitsubishi:melipc_mi5122-vw_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_l26cpu-\(p\)bt_firmware — cpe:2.3:o:mitsubishi:melsec_l26cpu-\(p\)bt_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_l26cpu\(-p\)_firmware — cpe:2.3:o:mitsubishi:melsec_l26cpu\(-p\)_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_l06cpu\(-p\)_firmware — cpe:2.3:o:mitsubishi:melsec_l06cpu\(-p\)_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_l02cpu\(-p\)_firmware — cpe:2.3:o:mitsubishi:melsec_l02cpu\(-p\)_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r08_cpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r08_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r16_cpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r16_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r32_cpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r32_cpu_firmware:*:*:*:*:*:*:*:*
mitsubishi melsec_iq-r_r120_cpu_firmware — cpe:2.3:o:mitsubishi:melsec_iq-r_r120_cpu_firmware:*:*:*:*:*:*:*:*

References for CVE-2021-20609

cvelogic Threat Intelligence