CVE-2026-1773: IEC 60870-5-104 used in RTU500: Potential Denial of Service impact on reception of invalid U-format frame. Pro

Q: How do I fix CVE-2026-1773?

rtu540 firmware: upgrade to 13.7.8; rtu560 firmware: upgrade to 13.7.8; rtu520 firmware: upgrade to 13.7.8. Exact commands for each OS are on this page.

Q: Is CVE-2026-1773 being exploited?

CVE-2026-1773 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-1773 affect?

CVE-2026-1773 affects rtu540 firmware, rtu560 firmware, rtu520 firmware. Severity is high (CVSS 7.5). IEC 60870-5-104 used in RTU500: Potential Denial of Service impact on reception of invalid U-format frame. Product is only affected if IEC 60870-5-104 bi-directional functionality is configured. Enabling secure communication following IEC 6

Q: How urgent is CVE-2026-1773?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADEUPGRADEUPGRADE

CVE-2026-1773 is a high-severity flaw (CVSS 7.5) affecting rtu540 firmware, rtu560 firmware, rtu520 firmware. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

IEC 60870-5-104 used in RTU500: Potential Denial of Service impact on reception of invalid U-format frame. Product is only affected if IEC 60870-5-104 bi-directional functionality is configured. Enabling secure communication following IEC 62351-3 does not remediate the vulnerability but mitigates the risk of exploitation.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 60%)
CISA exploited list	No
Weakness	CWE-184
Published	2026-02-24
Last modified	2026-06-17

Publisher (CNA): Hitachi Energy · Vendor: hitachienergy

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-02-24 14:16 UTCPublished CVE record published
2026-06-17 10:16 UTCUpdated Record last modified

hitachienergy rtu540 firmware UPGRADE

Affected: >= 12.7.1 and <= 12.7.7 · >= 13.5.1 and <= 13.5.4 · >= 13.6.1 and <= 13.6.2 · >= 13.7.1 and < 13.7.8 · 13.8.1

Fixed in: 13.7.8

Safe to downgrade to: a release before 12.7.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

hitachienergy rtu560 firmware UPGRADE

Affected: >= 12.7.1 and <= 12.7.7 · >= 13.5.1 and <= 13.5.4 · >= 13.6.1 and <= 13.6.2 · >= 13.7.1 and < 13.7.8 · 13.8.1

Fixed in: 13.7.8

Safe to downgrade to: a release before 12.7.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

hitachienergy rtu520 firmware UPGRADE

Affected: >= 12.7.1 and <= 12.7.7 · >= 13.5.1 and <= 13.5.4 · >= 13.6.1 and <= 13.6.2 · >= 13.7.1 and < 13.7.8 · 13.8.1

Fixed in: 13.7.8

Safe to downgrade to: a release before 12.7.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

hitachienergy rtu530 firmware UPGRADE

Affected: >= 12.7.1 and <= 12.7.7 · >= 13.5.1 and <= 13.5.4 · >= 13.6.1 and <= 13.6.2 · >= 13.7.1 and < 13.7.8 · 13.8.1

Fixed in: 13.7.8

Safe to downgrade to: a release before 12.7.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-1773?

rtu540 firmware: upgrade to 13.7.8; rtu560 firmware: upgrade to 13.7.8; rtu520 firmware: upgrade to 13.7.8. Exact commands for each OS are on this page.

Is CVE-2026-1773 being exploited?

CVE-2026-1773 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-1773 affect?

CVE-2026-1773 affects rtu540 firmware, rtu560 firmware, rtu520 firmware. Severity is high (CVSS 7.5). IEC 60870-5-104 used in RTU500: Potential Denial of Service impact on reception of invalid U-format frame. Product is only affected if IEC 60870-5-104 bi-directional functionality is configured. Enabling secure communication following IEC 6

How urgent is CVE-2026-1773?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-1772 MEDIUM 5.3 UPGRADE UPGRADE RTU500 web interface: An unprivileged user can read user management information

References

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