#VU54502 Insufficient Entropy in libtpms - CVE-2021-3505

Vulnerability identifier: #VU54502

Vulnerability risk: Low

CVSSv4.0: 0.4 [CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear]

CVE-ID: CVE-2021-3505

CWE-ID: CWE-331

Exploitation vector: Local

Exploit availability: No

Vulnerable software:
libtpms
Universal components / Libraries / Libraries used by multiple products

Vendor: Stefan Berger

Description

The vulnerability allows a local user to decrypt data.

The vulnerability exists in the TPM 2 implementation, which returns 2048 bit keys with ~1984 bit strength due to a bug in the TCG specification. The bug is in the key creation algorithm in RsaAdjustPrimeCandidate(), which is called before the prime number check.

Mitigation
Install updates from vendor's website.

Vulnerable software versions

libtpms: 0.5.2 - 0.7.8

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External links
https://bugzilla.redhat.com/show_bug.cgi?id=1950046
https://github.com/stefanberger/libtpms/issues/183
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/NUCZX4S53TUNTSGTCRDNOQZV2V2RI4RJ/

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Q & A

Can this vulnerability be exploited remotely?

No. This vulnerability can be exploited locally. The attacker should have authentication credentials and successfully authenticate on the system.

Is there known malware, which exploits this vulnerability?

No. We are not aware of malware exploiting this vulnerability.