How severe is CVE-2021-33586?

CVE-2021-33586 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.

Is CVE-2021-33586 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-33586?

CVE-2021-33586 affects Inspircd. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-33586?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-33586 published?

CVE-2021-33586 was published on 2021-05-27 and last updated on 2026-06-17.

CVE-2021-33586

CVE-2021-33586 is a medium-severity vulnerability in Inspircd with a CVSS 3.x base score of 4.3. 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-732.

Key facts

Severity: Medium (CVSS 3.x base score 4.3)
CVSS v2: 4.0
EPSS exploit prediction: 1% (55th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-732
Affected product: Inspircd
Published: 2021-05-27
Last modified: 2026-06-17

Description

InspIRCd 3.8.0 through 3.9.x before 3.10.0 allows any user (able to connect to the server) to access recently deallocated memory, aka the "malformed PONG" issue.

Frequently asked questions

What is CVE-2021-33586?: InspIRCd 3.8.0 through 3.9.x before 3.10.0 allows any user (able to connect to the server) to access recently deallocated memory, aka the "malformed PONG" issue.
How severe is CVE-2021-33586?: CVE-2021-33586 has a CVSS 3.x base score of 4.3, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
Is CVE-2021-33586 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (55th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-33586?: CVE-2021-33586 affects Inspircd. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-33586?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-33586 published?: CVE-2021-33586 was published on 2021-05-27 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:inspircd:inspircd:*:*:*:*:*:*:*:*

More vulnerabilities in Inspircd

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CVE-2020-25269 — Medium (CVSS 6.5): An issue was discovered in InspIRCd 2 before 2.0.29 and 3 before 3.6.0. The pgsql module contains a use after free…
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