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.

Published: 2021-05-27 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-33586 is rated Low Risk (37/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 0.89%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-33586

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.19% 0.89% +0.70%
2 2025-06-04 0.29% 0.19% -0.10%
3 2025-03-30 — 0.29% —

Full EPSS history (11 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-33586

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.8 1.4 [email protected]
4.0 2.0 MEDIUM
AV:N/AC:L/Au:S/C:P/I:N/A:N Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:S)
A single authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 8.0 2.9 [email protected]

Weakness enumeration for CVE-2021-33586

OS Trackers for CVE-2021-33586

vendor priority summary link
alpine medium CVE-2021-33586: 1 source package rows (inspircd); 4 state rows across 4 repos (3.20-community, 3.21-community, 3.22-community, edge-community); fixed 4, open 0. https://security.alpinelinux.org/vuln/CVE-2021-33586
debian not yet assigned CVE-2021-33586 not yet assigned priority: Debian including 1 source packages (inspircd), 4 status rows across 4 suites (bookworm, bullseye, sid, trixie): resolved 4. https://security-tracker.debian.org/tracker/CVE-2021-33586
gentoo low CVE-2021-33586: 1 GLSA(s) (202107-22), 1 atom(s) (net-irc/inspircd); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-33586
ubuntu medium CVE-2021-33586 medium priority: Ubuntu including 1 source packages (inspircd), 14 status rows across 14 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, trusty, upstream, xenial): not-affected 8, ignored 4, DNE 1, released 1. https://ubuntu.com/security/CVE-2021-33586

Affected software / configurations for CVE-2021-33586

Vendor Product Version Raw CPE
inspircd inspircd >= 3.8.0, < 3.10.0 cpe:2.3:a:inspircd:inspircd:*:*:*:*:*:*:*:*

References for CVE-2021-33586

cvelogic Threat Intelligence