CVE-2026-89763
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk2th percentile - higher than 2% of all known CVEs
Summary
A use-after-free vulnerability exists in the Linux kernel's trusted keys (KEYS: trusted) module due to incorrect TPM teardown ordering. The trusted_tpm_exit() function drops the TPM chip reference and frees the digest array before unregistering the trusted key type, allowing a concurrent key operation to dereference freed memory.
Risk Assessment
This can cause kernel memory corruption, system crashes (panic), or potentially local privilege escalation. Exploitation requires the ability to trigger trusted key operations while the module is being unloaded.
Recommendation
Update the Linux kernel to a version containing the fix that moves unregister_key_type() before releasing TPM resources. Until patched, restrict module unloading of trusted and limit trusted key operations to trusted users.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: KEYS: trusted: Fix TPM teardown ordering trusted_tpm_exit() drops the TPM chip reference and frees the digest array before unregistering the trusted key type. key_type_lookup() holds key_types_sem for reading until the key operation finishes, while unregister_key_type() takes it for writing. It therefore provides the synchronization point that must precede backend teardown. The current order permits this interleaving: CPU 0 CPU 1 trusted_tpm_exit() key_type_lookup("trusted") put_device(&chip->dev) trusted_tpm_seal() kfree(digests) pcrlock() unregister_key_type() tpm_pcr_extend(..., digests) CPU 1 can consequently dereference the freed digest array. The chip can also be released before callbacks stop using it. KASAN reported: BUG: KASAN: slab-use-after-free in tpm_pcr_extend+0x1f0/0x200 Read of size 2 at addr ffff88810872d000 by task poc/89 Call Trace: tpm_pcr_extend+0x1f0/0x200 pcrlock+0x42/0x70 [trusted] trusted_tpm_seal+0x1b6/0x570 [trusted] trusted_instantiate+0x293/0x340 [trusted] __key_instantiate_and_link+0xb2/0x2b0 __key_create_or_update+0x61e/0xb50 __do_sys_add_key+0x1b8/0x310 Allocated by task 88: __kmalloc_noprof+0x1a7/0x490 do_one_initcall+0xa1/0x390 do_init_module+0x2df/0x840 Freed by task 90: kfree+0x131/0x3c0 trusted_tpm_exit+0x59/0xa0 [trusted] __do_sys_delete_module+0x346/0x510 Move unregister_key_type() before releasing either resource. This stops new lookups and waits for in-flight key operations to finish before the backend state is destroyed.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS