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

Vulnerability summary

CVE-2026-85769 is a medium (CVSS 6.5) Out-of-bounds Read vulnerability in libtpms. EPSS estimates a 0.42% chance of exploitation in the next 30 days, higher than 35.2% of scored vulnerabilities.

Timeline

1. 04-09-2026
   PublishedVulnerability first disclosed.
2. 09-09-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.