CVE-2021-3623 [Medium] | Out-of-bounds Write in Libtpms

A flaw was found in libtpms. The flaw can be triggered by specially-crafted TPM 2 command packets containing illegal values and may lead to an out-of-bounds access when the volatile state of the TPM 2 is marshalled/written or unmarshalled/read. The highest threat from this vulnerability is to system availability.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-12-16	0.04%	0.05%	+0.01%
2	2025-11-21	0.08%	0.04%	-0.03%
3	2025-11-18	—	0.08%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-12-16

0.04%

0.05%

+0.01%

2025-11-21

0.08%

0.04%

-0.03%

2025-11-18

—

0.08%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
6.1	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/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: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:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	4.2	[email protected]
3.6	2.0	LOW	`AV:L/AC:L/Au:N/C:P/I:N/A:P` Click to expand Access vector (AV:L) Requires local access to the target system. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	3.9	4.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

6.1

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:N/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: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:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

4.2

[email protected]

3.6

2.0

LOW

AV:L/AC:L/Au:N/C:P/I:N/A:P Click to expand

Access vector (AV:L): Requires local access to the target system.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

3.9

4.9

[email protected]

OS Trackers for CVE-2021-3623

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2021-3623 not yet assigned priority: Debian including 1 source packages (libtpms), 4 status rows across 4 suites (bookworm, forky, sid, trixie): resolved 4.	https://security-tracker.debian.org/tracker/CVE-2021-3623
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-3623
`suse`	medium	CVE-2021-3623 severity moderate: SUSE including 11 source package names (0.58.0.20.46:libtpms0-0.8.2-150300.3.6.1, libtpms-devel-0.8.2-150300.3.6.1, …), 27 product×package rows across 19 product lines (Container suse/sles/15.5/virt-launcher, SUSE Linux Enterprise Micro 5.1, … (19 product lines)): Fixed 27.	https://www.suse.com/security/cve/CVE-2021-3623/
`ubuntu`	medium	CVE-2021-3623 medium priority: Ubuntu including 1 source packages (libtpms), 9 status rows across 9 suites (bionic, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): ignored 4, DNE 3, not-affected 1, released 1.	https://ubuntu.com/security/CVE-2021-3623

Affected software / configurations for CVE-2021-3623

Vendor	Product	Version	Raw CPE
libtpms_project	libtpms	< 0.6.5	cpe:2.3:a:libtpms_project:libtpms::::::::
libtpms_project	libtpms	>= 0.7.0, < 0.7.8	cpe:2.3:a:libtpms_project:libtpms::::::::
libtpms_project	libtpms	>= 0.8.0, < 0.8.4	cpe:2.3:a:libtpms_project:libtpms::::::::
redhat	enterprise_linux	8.0	cpe:2.3:o:redhat:enterprise_linux:8.0::::advanced_virtualization:::
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*

References for CVE-2021-3623

URL	Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1976806	Issue Tracking Patch Third Party Advisory
https://github.com/stefanberger/libtpms/commit/2e6173c	Patch Third Party Advisory
https://github.com/stefanberger/libtpms/commit/2f30d62	Patch Third Party Advisory
https://github.com/stefanberger/libtpms/commit/7981d9a	Patch Third Party Advisory
https://github.com/stefanberger/libtpms/pull/223	Issue Tracking Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/Z7KZSYMTE7Z4BBEZUWO2DIMQDWMGEP46/

URL

CVE-2021-3623

Exploit prediction scoring system (EPSS) score for CVE-2021-3623

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3623

Weakness enumeration for CVE-2021-3623

OS Trackers for CVE-2021-3623

Affected software / configurations for CVE-2021-3623

References for CVE-2021-3623