How severe is CVE-2021-31819?

CVE-2021-31819 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-2021-31819 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-31819?

CVE-2021-31819 affects Octopus Halibut. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-31819?

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-2021-31819 published?

CVE-2021-31819 was published on 2021-09-22 and last updated on 2026-06-17.

CVE-2021-31819

CVE-2021-31819 is a critical-severity vulnerability in Octopus Halibut 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-502.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 2% (81st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-502
Affected product: Octopus Halibut
Published: 2021-09-22
Last modified: 2026-06-17

Description

In Halibut versions prior to 4.4.7 there is a deserialisation vulnerability that could allow remote code execution on systems that already trust each other based on certificate verification.

Frequently asked questions

What is CVE-2021-31819?: In Halibut versions prior to 4.4.7 there is a deserialisation vulnerability that could allow remote code execution on systems that already trust each other based on certificate verification.
How severe is CVE-2021-31819?: CVE-2021-31819 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-2021-31819 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (81st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-31819?: CVE-2021-31819 affects Octopus Halibut. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-31819?: 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-2021-31819 published?: CVE-2021-31819 was published on 2021-09-22 and last updated on 2026-06-17.

References

https://advisories.octopus.com/adv/2021-08---Remote-Code-Execution-via-Deserialisation-in-the-Halibut-Protocol-%28CVE-2021-31819%29.2250309681.html

Affected products (1)

cpe:2.3:a:octopus:halibut:*:*:*:*:*:*:*:*

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