CVE-2021-42386

A use-after-free in Busybox's awk applet leads to denial of service and possibly code execution when processing a crafted awk pattern in the nvalloc function

Published: 2021-11-15 Last update: 2025-11-03 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-42386 is rated Moderate Risk (45.9/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.29%). Review affected assets and schedule remediation.

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-2021-42386

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 2025-11-21 1.53% 0.29% -1.24%
2 2025-11-18 0.29% 1.53% +1.24%
3 2025-11-04 — 0.29% —

Full EPSS history (15 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42386

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.2 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H 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:H)
They need powerful rights—admin, root, or similar—before this pays off.
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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.2 5.9 [email protected]
7.2 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:H/I:H/A:H 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:H)
They need powerful rights—admin, root, or similar—before this pays off.
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:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.2 5.9 134c704f-9b21-4f2e-91b3-4a467353bcc0
6.5 2.0 MEDIUM
AV:N/AC:L/Au:S/C:P/I:P/A:P 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:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.0 6.4 [email protected]

Weakness enumeration for CVE-2021-42386

OS Trackers for CVE-2021-42386

vendor priority summary link
alpine — CVE-2021-42386: 1 source package rows (busybox); 36 state rows across 9 repos (3.11-main, 3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 11, open 25. https://security.alpinelinux.org/vuln/CVE-2021-42386
debian not yet assigned CVE-2021-42386 not yet assigned priority: Debian including 1 source packages (busybox), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-42386
gentoo normal CVE-2021-42386: 1 GLSA(s) (202407-17), 1 atom(s) (sys-apps/busybox); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-42386
redhat medium — https://access.redhat.com/security/cve/CVE-2021-42386
suse medium CVE-2021-42386 severity moderate: SUSE including 20 source package names (1.34.1:busybox-1.34.1-4.9.1, 15.4:busybox-1.35.0-150400.3.3.1, …), 80 product×package rows across 51 product lines (Container bci/bci-busybox, Container caasp/v4/busybox, … (51 product lines)): Fixed 73, Known Not Affected 7. https://www.suse.com/security/cve/CVE-2021-42386/
ubuntu low CVE-2021-42386 low priority: Ubuntu including 1 source packages (busybox), 8 status rows across 8 suites (bionic, focal, hirsute, impish, jammy, trusty, upstream, xenial): released 6, ignored 2. https://ubuntu.com/security/CVE-2021-42386

Affected software / configurations for CVE-2021-42386

Vendor Product Version Raw CPE
busybox busybox >= 1.16.0, <= 1.33.1 cpe:2.3:a:busybox:busybox:*:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*

References for CVE-2021-42386

cvelogic Threat Intelligence