# CVE-2026-85769: Libtpms: libtpms: heap out-of-bounds read in tpm2 state unmarshalling via unchecked block_skip_read() blocksize

Status: published. Published: 2026-09-04. Updated: 2026-11-06.

A flaw was found in libtpms, a library that provides software TPM 2.0 emulation. When restoring TPM 2.0 state (for example during a virtual machine's power-on or state/migration restore), a malformed state blob can supply an oversized skip-block length that is not validated against the remaining size of the input buffer. This can drive an internal size counter negative, which bypasses a subsequent bounds check due to an unsafe signed-to-unsigned conversion, causing the parser to read memory outside the bounds of the heap buffer holding the state data. Successful exploitation can crash the process hosting libtpms (such as swtpm), resulting in a denial of service of the emulated TPM device and the virtual machine that depends on it. No data corruption or information disclosure was confirmed.

## Remediation

- workaround: No mitigation is currently available that meets Red Hat Product Security's standards for usability, deployment, applicability, or stability. (source: CNA: redhat)

## Affected products and versions

- Red Hat / Red Hat Enterprise Linux 10 (libtpms): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (virt:rhel/libtpms): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (libtpms): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 6.5 (medium); CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H; source: CNA: redhat

- CISA KEV: No listing in collected sources

- EPSS: 0.42% as of 2026-11-05; percentile 36.52%

- SSVC: exploitation none; automatable no; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-125

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/security/cve/CVE-2026-85769 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2528538 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://github.com/stefanberger/libtpms/commit/b1462888180d896af03cae0487e8d45009cc445e (CNA: redhat)

- https://github.com/stefanberger/libtpms/issues/614 (CNA: redhat)

- https://github.com/stefanberger/libtpms/pull/613 (CNA: redhat)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-85769; retrieved 2026-11-06; source updated 2026-11-06

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-85769; retrieved 2026-11-06; source updated Not reported

Revision: 7a629fb00a86c00349cde9f74be6eb02adf738d3c94440de0fd4533cde5ef80c

Canonical: https://y2.dev/cve/CVE-2026-85769

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