CVE-2021-3700

A use-after-free vulnerability was found in usbredir in versions prior to 0.11.0 in the usbredirparser_serialize() in usbredirparser/usbredirparser.c. This issue occurs when serializing large amounts of buffered write data in the case of a slow or blocked destination.

Published: 2022-02-24 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-3700 is rated Low Risk (33.3/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.30%). 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-2021-3700

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 0.13% 0.30% +0.17%
2 2026-05-27 0.04% 0.13% +0.09%
3 2025-11-21 — 0.04% —

Full EPSS history (8 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3700

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.4 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:H/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
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.
 0.5 5.9 [email protected]
4.4 2.0 MEDIUM
AV:L/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:L)
Requires local access to the target system.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 3.4 6.4 [email protected]

Weakness enumeration for CVE-2021-3700

OS Trackers for CVE-2021-3700

vendor priority summary link
alpine medium CVE-2021-3700: 1 source package rows (usbredir); 8 state rows across 8 repos (3.12-main, 3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 7, open 1. https://security.alpinelinux.org/vuln/CVE-2021-3700
debian not yet assigned CVE-2021-3700 not yet assigned priority: Debian including 1 source packages (usbredir), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 4, open 1. https://security-tracker.debian.org/tracker/CVE-2021-3700
redhat low — https://access.redhat.com/security/cve/CVE-2021-3700
suse low CVE-2021-3700 severity low: SUSE including 11 source package names (libusbredirhost1, libusbredirhost1-0.11.0-1.2, …), 158 product×package rows across 58 product lines (SUSE CaaS Platform 4.0, SUSE CaaS Platform 4.5, … (58 product lines)): Known Not Affected 151, Fixed 7. https://www.suse.com/security/cve/CVE-2021-3700/
ubuntu low CVE-2021-3700 low priority: Ubuntu including 1 source packages (usbredir), 9 status rows across 9 suites (bionic, focal, hirsute, impish, jammy, kinetic, trusty, upstream, xenial): released 5, ignored 2, not-affected 2. https://ubuntu.com/security/CVE-2021-3700

Affected software / configurations for CVE-2021-3700

Vendor Product Version Raw CPE
spice-space usbredir < 0.11.0 cpe:2.3:a:spice-space:usbredir:*:*:*:*:*:*:*:*
redhat enterprise_linux 6.0 cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*
redhat enterprise_linux 7.0 cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*
redhat enterprise_linux 8.0 cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
debian debian_linux 9.0 cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*

References for CVE-2021-3700

cvelogic Threat Intelligence