Executive brief
The Linux kernel's TPM (Trusted Platform Module) driver contains a use-after-free vulnerability in the cryptographic key agreement code. When the system requests entropy for random number generation, it invokes cryptographic operations on freed memory structures, causing the kernel to crash or potentially execute arbitrary code. This affects any system using TPM-based security features and modern cryptographic accelerators.
Technical details
A use-after-free vulnerability exists in tpm_buf_append_salt() (drivers/char/tpm/tpm2-sessions.c) where calls to crypto_kpp_generate_public_key() and crypto_kpp_compute_shared_secret() are made without installing a completion callback. The function immediately frees the kpp_request via kpp_request_free() while discarding return values. When the ecdh-nist-p256 KPP backend is asynchronous (atmel-ecc, HPRE, keembay-ocs), these operations return -EINPROGRESS, causing a deferred completion worker to dereference the already-freed request. The vulnerability is automatically triggered via the hwrng_fillfn kernel thread on every entropy poll without requiring user action. The fix wraps both KPP operations in crypto_wait_req() with proper completion callbacks and error propagation; the wait is a no-op for synchronous backends. Patches are available in Linux 6.10+.
Affected products
- Linux Linux kernel 6.10+
Timeline
- 2026-08-15: disclosed
- 2026-07-24: patched