How severe is CVE-2021-21777?

CVE-2021-21777 has a CVSS 3.x base score of 10.0, 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 none, and availability high.

Is CVE-2021-21777 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21777?

CVE-2021-21777 affects Opener Project Opener. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-21777?

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-2021-21777 published?

CVE-2021-21777 was published on 2021-06-17 and last updated on 2026-06-17.

CVE-2021-21777

CVE-2021-21777 is a critical-severity vulnerability in Opener Project Opener with a CVSS 3.x base score of 10.0. 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-125.

Key facts

Severity: Critical (CVSS 3.x base score 10.0)
CVSS v2: 9.4
EPSS exploit prediction: 2% (75th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-125
Affected product: Opener Project Opener
Published: 2021-06-17
Last modified: 2026-06-17

Description

An information disclosure vulnerability exists in the Ethernet/IP UDP handler functionality of EIP Stack Group OpENer 2.3 and development commit 8c73bf3. A specially crafted network request can lead to an out-of-bounds read.

Frequently asked questions

What is CVE-2021-21777?: An information disclosure vulnerability exists in the Ethernet/IP UDP handler functionality of EIP Stack Group OpENer 2.3 and development commit 8c73bf3. A specially crafted network request can lead to an out-of-bounds read.
How severe is CVE-2021-21777?: CVE-2021-21777 has a CVSS 3.x base score of 10.0, 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 none, and availability high.
Is CVE-2021-21777 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21777?: CVE-2021-21777 affects Opener Project Opener. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21777?: 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-2021-21777 published?: CVE-2021-21777 was published on 2021-06-17 and last updated on 2026-06-17.

References

https://talosintelligence.com/vulnerability_reports/TALOS-2021-1234

Affected products (1)

cpe:2.3:a:opener_project:opener:2.3:*:*:*:*:*:*:*

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