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CVE-2026-72151
tpm: tpm2-sessions: wait for async KPP completion in tpm_buf_append_salt
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/char. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-72151 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
tpm_buf_append_salt() in drivers/char/tpm/tpm2-sessions.c calls crypto_kpp_generate_public_key() and crypto_kpp_compute_shared_secret() without installing a completion callback, discards both return values, and immediately frees the kpp_request via kpp_request_free(). When the resolved ecdh-nist-p256 KPP backend is asynchronous (atmel-ecc, HPRE, keembay-ocs), either operation returns -EINPROGRESS and the deferred completion worker dereferences the freed request. The path fires automatically from the hwrng_fillfn kernel thread via tpm_get_random -> tpm2_get_random -> tpm2_start_auth_session -> tpm_buf_append_salt on every entropy poll, without any userland action. Install crypto_req_done as the completion callback, wrap both KPP operations in crypto_wait_req(), and propagate errors to the caller. The wait is a no-op for synchronous backends.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
drivers/char/tpm/tpm2-sessions.c
- What this is
- TPM DEVICE DRIVERMAINTAINERS section matched on drivers/char/tpm/ · linux-integrity@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_TCG_TPM /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian builds this code. Every release with an answer below compiles the affected file into the kernels it ships. The build rule could not be established for 1 release, so nothing is claimed about those.
- bookworm?
- trixie, forky, sidy
- ?
- not established - no Makefile entry for the affected file
- y
- built into the kernel image on every flavour - only a patch removes it
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switch
- CONFIG_TCG_TPM
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 8.4 high
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.20%, higher than 8.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/char
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.10 | 6.12.97 | 111e520efbe8 |
| 6.10 | 6.18.40 | 934d1cd40e28 |
| 6.10 | 7.1.5 | 493333f16792 |
| 6.10 | 7.2 | 73851a7c43df |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:LAttack vector, local
- The vulnerable code is reached only via local kernel TPM/HWRNG paths (hwrng_fillfn kernel thread polling tpm_get_random, or local /dev/hwrng reads); there is no network, adjacent-radio, or physical-access entry point to tpm_buf_append_salt.
- AC:LAttack complexity, low
- On affected builds (CONFIG_TCG_TPM2_HMAC plus an async ecdh-nist-p256 backend), the UAF is deterministically triggered each auth-session setup without winning a race; async KPP returns -EINPROGRESS and the completion worker later dereferences the already-freed kpp_request.
- PR:NPrivileges required, none
- No attacker credentials are required: the hwrng kernel thread invokes tpm2_start_auth_session automatically on TPM RNG polls, and unprivileged local processes can also reach tpm_get_random via /dev/hwrng without root or namespaced admin capabilities.
- UI:NUser interaction, none
- Exploitation does not require any victim user action such as mounting a filesystem or opening a file; the bug fires from background kernel entropy collection and TPM session setup without interactive steps.
- S:UScope, unchanged
- Impact is confined to kernel memory integrity and availability on the same host; it is a standard kernel heap UAF, not a cross-boundary escape such as guest-to-host VM breakout or IOMMU/DMA bypass.
- C:HConfidentiality impact, high
- Use-after-free of a kmalloc'd kpp_request lets an attacker influence freed heap contents and potentially obtain arbitrary kernel memory read primitives through heap grooming, not merely a bounded leak.
- I:HIntegrity impact, high
- The UAF corrupts kernel heap metadata/object lifetimes and can be leveraged for arbitrary write or control-flow hijack (privilege escalation), not just limited or transient data modification.
- A:HAvailability impact, high
- The deferred crypto completion dereferences freed memory, causing kernel oops/panic or hang during normal TPM RNG polling, yielding complete loss of system availability on affected hardware.