How severe is CVE-2021-27734?

CVE-2021-27734 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-27734 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-27734?

CVE-2021-27734 primarily affects Belden Hirschmann Hios. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-27734?

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

When was CVE-2021-27734 published?

CVE-2021-27734 was published on 2021-05-17 and last updated on 2026-06-17.

CVE-2021-27734

CVE-2021-27734 is a critical-severity vulnerability in Belden Hirschmann Hios with a CVSS 3.x base score of 9.8. 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-287.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 1% (66th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-287
Affected product: Belden Hirschmann Hios
Published: 2021-05-17
Last modified: 2026-06-17

Description

Hirschmann HiOS 07.1.01, 07.1.02, and 08.1.00 through 08.5.xx and HiSecOS 03.3.00 through 03.5.01 allow remote attackers to change the credentials of existing users.

Frequently asked questions

What is CVE-2021-27734?: Hirschmann HiOS 07.1.01, 07.1.02, and 08.1.00 through 08.5.xx and HiSecOS 03.3.00 through 03.5.01 allow remote attackers to change the credentials of existing users.
How severe is CVE-2021-27734?: CVE-2021-27734 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27734 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (66th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27734?: CVE-2021-27734 primarily affects Belden Hirschmann Hios. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-27734?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-27734 published?: CVE-2021-27734 was published on 2021-05-17 and last updated on 2026-06-17.

References

https://dam.belden.com/dmm3bwsv3/assetstream.aspx?assetid=12914&mediaformatid=50063&destinationid=10016

Affected products (4)

cpe:2.3:o:belden:hirschmann_hios:*:*:*:*:*:*:*:*
cpe:2.3:o:belden:hirschmann_hios:07.1.01:*:*:*:*:*:*:*
cpe:2.3:o:belden:hirschmann_hios:07.1.02:*:*:*:*:*:*:*
cpe:2.3:o:belden:hisecos:*:*:*:*:*:*:*:*

More vulnerabilities in Belden Hirschmann Hios

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CVE-2019-12255 — Critical (CVSS 9.8): Wind River VxWorks has a Buffer Overflow in the TCP component (issue 1 of 4). This is a IPNET security vulnerability:…
CVE-2019-12256 — Critical (CVSS 9.8): Wind River VxWorks 6.9 and vx7 has a Buffer Overflow in the IPv4 component. There is an IPNET security vulnerability:…

All CVEs affecting Belden Hirschmann Hios →

Other CWE-287 (Improper Authentication) vulnerabilities

CVE-2026-45480 — Critical (CVSS 10.0): Improper authentication in Azure Active Directory allows an unauthorized attacker to elevate privileges over a network.
CVE-2026-46389 — Critical (CVSS 10.0): UDS Identity Config builds the Keycloak configuration image (realm, plugins, theme, truststore, JARs) consumed by UDS…
CVE-2026-10611 — Critical (CVSS 10.0): An authentication bypass vulnerability exists in MISP when LDAP mixed authentication is enabled with OTP enforcement.…
CVE-2026-47280 — Critical (CVSS 10.0): Improper authentication in Azure Resource Manager (ARM) allows an unauthorized attacker to elevate privileges over a…
CVE-2026-42822 — Critical (CVSS 10.0): Improper authentication in Azure Local Disconnected Operations allows an unauthorized attacker to elevate privileges…
CVE-2026-20182 — Critical (CVSS 10.0): May 2026: This security advisory provides the details and fix information for a vulnerability that was discovered and…

Browse all CWE-287 (Improper Authentication) vulnerabilities →