CVE-2021-3505

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2021-04-19 · updated 2026-06-17
Weakness: CWE-331

Description

A flaw was found in libtpms in versions before 0.8.0. The TPM 2 implementation 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. The highest threat from this vulnerability is to data confidentiality.

Affected products

Fedoraproject Fedora: 33
stefanberger libtpms: before 0.8.0 — fixed in 0.8.0
Red Hat Enterprise Linux: 8.0

How to fix

Upgrade to a fixed version: stefanberger libtpms 0.8.0. Check the vendor advisory for mitigations.

References

https://bugzilla.redhat.com/show_bug.cgi?id=1950046
https://github.com/stefanberger/libtpms/issues/183
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NUCZX4S53TUNTSGTCRDNOQZV2V2RI4RJ/
https://bugzilla.redhat.com/show_bug.cgi?id=1950046
https://github.com/stefanberger/libtpms/issues/183
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/NUCZX4S53TUNTSGTCRDNOQZV2V2RI4RJ/

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