CVE-2021-36976

libarchive 3.4.1 through 3.5.1 has a use-after-free in copy_string (called from do_uncompress_block and process_block).

Published: 2021-07-20 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-36976 is rated Moderate Risk (58.3/100): CVSS Medium severity, with medium exploitation likelihood (EPSS 2.84%). EPSS rose +2.66% over the last day, indicating growing attacker interest. 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-2021-36976

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 0.18% 2.84% +2.66%
2 2025-12-21 0.10% 0.18% +0.08%
3 2025-11-21 — 0.10% —

Full EPSS history (17 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-36976

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.5 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/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:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R)
A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 2.8 3.6 [email protected]
4.3 2.0 MEDIUM
AV:N/AC:M/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 2.9 [email protected]

Weakness enumeration for CVE-2021-36976

OS Trackers for CVE-2021-36976

vendor priority summary link
alpine — CVE-2021-36976: 1 source package rows (libarchive); 15 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 8, open 7. https://security.alpinelinux.org/vuln/CVE-2021-36976
debian not yet assigned CVE-2021-36976 not yet assigned priority: Debian including 1 source packages (libarchive), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-36976
gentoo high CVE-2021-36976: 1 GLSA(s) (202208-26), 1 atom(s) (app-arch/libarchive); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-36976
redhat medium — https://access.redhat.com/security/cve/CVE-2021-36976
suse medium CVE-2021-36976 severity moderate: SUSE including 259 source package names (amazon/suse-sles-15-sp1-chost-byos-v20210304-hvm-ssd-x86_64, amazon/suse-sles-15-sp1-chost-byos-v20220127-hvm-ssd-x86_64, …), 387 product×package rows across 91 product lines (HPE Helion OpenStack 8, Image SLES15-SP3-EC2-HVM, … (91 product lines)): Known Affected 231, Fixed 87, Known Not Affected 69. https://www.suse.com/security/cve/CVE-2021-36976/
ubuntu medium CVE-2021-36976 medium priority: Ubuntu including 1 source packages (libarchive), 9 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 3, released 3, ignored 2, needs-triage 1. https://ubuntu.com/security/CVE-2021-36976

Affected software / configurations for CVE-2021-36976

Vendor Product Version Raw CPE
libarchive libarchive >= 3.4.1, <= 3.5.2 cpe:2.3:a:libarchive:libarchive:*:*:*:*:*:*:*:*
fedoraproject fedora 35 cpe:2.3:o:fedoraproject:fedora:35:*:*:*:*:*:*:*
apple ipados < 15.4 cpe:2.3:o:apple:ipados:*:*:*:*:*:*:*:*
apple iphone_os < 15.4 cpe:2.3:o:apple:iphone_os:*:*:*:*:*:*:*:*
apple macos < 12.3 cpe:2.3:o:apple:macos:*:*:*:*:*:*:*:*
apple watchos < 8.5 cpe:2.3:o:apple:watchos:*:*:*:*:*:*:*:*
splunk universal_forwarder >= 8.2.0, < 8.2.12 cpe:2.3:a:splunk:universal_forwarder:*:*:*:*:*:*:*:*
splunk universal_forwarder >= 9.0.0, < 9.0.6 cpe:2.3:a:splunk:universal_forwarder:*:*:*:*:*:*:*:*
splunk universal_forwarder 9.1.0 cpe:2.3:a:splunk:universal_forwarder:9.1.0:*:*:*:*:*:*:*

References for CVE-2021-36976

URL Tags
http://seclists.org/fulldisclosure/2022/Mar/27 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2022/Mar/28 Mailing List Third Party Advisory
http://seclists.org/fulldisclosure/2022/Mar/29 Mailing List Third Party Advisory
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=32375 Issue Tracking Third Party Advisory
https://github.com/google/oss-fuzz-vulns/blob/main/vulns/libarchive/OSV-2021-557.yaml Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/SE5NJQNM22ZE5Z55LPAGCUHSBQZBKMKC/ Mailing List Third Party Advisory
https://security.gentoo.org/glsa/202208-26 Third Party Advisory
https://support.apple.com/kb/HT213182 Third Party Advisory
https://support.apple.com/kb/HT213183 Third Party Advisory
https://support.apple.com/kb/HT213193 Third Party Advisory
https://lists.debian.org/debian-lts-announce/2024/11/msg00007.html
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