How severe is CVE-2021-35533?

CVE-2021-35533 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-35533 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-35533?

CVE-2021-35533 primarily affects Hitachienergy Rtu500 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-35533?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-35533 published?

CVE-2021-35533 was published on 2021-11-26 and last updated on 2026-06-17.

CVE-2021-35533

CVE-2021-35533 is a high-severity vulnerability in Hitachienergy Rtu500 Firmware with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-20.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 7.1
EPSS exploit prediction: 1% (56th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Hitachienergy Rtu500 Firmware
Published: 2021-11-26
Last modified: 2026-06-17

Description

Improper Input Validation vulnerability in the APDU parser in the Bidirectional Communication Interface (BCI) IEC 60870-5-104 function of Hitachi Energy RTU500 series allows an attacker to cause the receiving RTU500 CMU of which the BCI is enabled to reboot when receiving a specially crafted message. By default, BCI IEC 60870-5-104 function is disabled (not configured). This issue affects: Hitachi Energy RTU500 series CMU Firmware version 12.0.* (all versions); CMU Firmware version 12.2.* (all versions); CMU Firmware version 12.4.* (all versions).

Frequently asked questions

What is CVE-2021-35533?: Improper Input Validation vulnerability in the APDU parser in the Bidirectional Communication Interface (BCI) IEC 60870-5-104 function of Hitachi Energy RTU500 series allows an attacker to cause the receiving RTU500 CMU of which the BCI is enabled to reboot when receiving a specially crafted message. By default, BCI IEC 60870-5-104 function is disabled (not configured). This issue affects: Hitachi Energy RTU500 series CMU Firmware version 12.0.* (all versions); CMU Firmware version 12.2.* (all versions); CMU Firmware version 12.4.* (all versions).
How severe is CVE-2021-35533?: CVE-2021-35533 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-35533 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (56th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-35533?: CVE-2021-35533 primarily affects Hitachienergy Rtu500 Firmware. In total, 3 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-35533?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-35533 published?: CVE-2021-35533 was published on 2021-11-26 and last updated on 2026-06-17.

References

https://search.abb.com/library/Download.aspx?DocumentID=8DBD000063&LanguageCode=en&DocumentPartId=&Action=Launch

Affected products (3)

cpe:2.3:o:hitachienergy:rtu500_firmware:12.0:*:*:*:*:*:*:*
cpe:2.3:o:hitachienergy:rtu500_firmware:12.2:*:*:*:*:*:*:*
cpe:2.3:o:hitachienergy:rtu500_firmware:12.4:*:*:*:*:*:*:*

More vulnerabilities in Hitachienergy Rtu500 Firmware

CVE-2022-4608 — High (CVSS 7.5): A vulnerability exists in HCI IEC 60870-5-104 function included in certain versions of the RTU500 series product. The…
CVE-2022-2502 — High (CVSS 7.5): A vulnerability exists in the HCI IEC 60870-5-104 function included in certain versions of the RTU500 series product.…
CVE-2022-28613 — High (CVSS 7.5): A vulnerability exists in the HCI Modbus TCP function included in the product versions listed above. If the HCI Modbus…
CVE-2021-27196 — High (CVSS 7.5): Improper Input Validation vulnerability in Hitachi ABB Power Grids Relion 670 Series, Relion 670/650 Series, Relion…
CVE-2023-6711 — Medium (CVSS 5.9): Vulnerability exists in SCI IEC 60870-5-104 and HCI IEC 60870-5-104 that affects the RTU500 series product versions…
CVE-2022-3353 — Medium (CVSS 5.9): A vulnerability exists in the IEC 61850 communication stack that affects multiple Hitachi Energy products. An…

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