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CVE-2026-72135
tpm: Make the TPM character devices non-seekable
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/char. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72135 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| 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
The TPM character devices expose a sequential command/response interface, but their open handlers leave FMODE_PREAD and FMODE_PWRITE enabled. After a command leaves a response pending, pread(fd, buf, 16, 0x1400) passes 0x1400 as *off to tpm_common_read(). The transfer length is bounded by response_length, but the offset is used unchecked when forming data_buffer + *off. A sufficiently large offset therefore causes an out-of-bounds heap read through copy_to_user() and, if the copy succeeds, an out-of-bounds zero-write through the following memset(). Positional I/O does not provide coherent semantics for this interface. An arbitrary pread offset cannot represent how much of a response has been consumed sequentially. The write callback always stores a command at the start of data_buffer, while pwrite() does not update file->f_pos and can leave the sequential read cursor stale. Call nonseekable_open() from both open handlers. This removes FMODE_PREAD and FMODE_PWRITE, causing positional reads and writes to fail with -ESPIPE before reaching the TPM callbacks, and explicitly marks the files non-seekable. Normal read() and write() continue to use the existing sequential f_pos cursor, leaving the response state machine unchanged. Tested on Linux 6.12 with KASAN and a swtpm TPM2 device: - sequential partial reads returned the complete response - pread() and preadv() with offset 0x1400 returned -ESPIPE - pwrite() and pwritev() with offset zero returned -ESPIPE - the pending response remained intact after the rejected operations - a subsequent normal command/response cycle completed normally - no KASAN report was produced.
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/tpm-dev.c
drivers/char/tpm/tpmrm-dev.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 below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- 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
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.17%, higher than 5.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- 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 |
|---|---|---|
| 5.0 | 5.10.261 | ed0ffc2c0166 |
| 5.0 | 5.15.212 | 232dcf908eb7 |
| 5.0 | 6.1.178 | dda695fab5e2 |
| 5.0 | 6.6.145 | 9c513dabd454 |
| 5.0 | 6.12.97 | 21a13f932972 |
| 5.0 | 6.18.40 | ada4b9a5087e |
| 5.0 | 7.1.5 | 947b773caaa5 |
| 5.0 | 7.2 | f20d61c22bca |
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
- Exploitation requires local pread()/write() syscalls on /dev/tpm0 or /dev/tpmrm0 character devices; there is no network, Bluetooth, or physical-bus code path to the vulnerable tpm_common_read() handler.
- AC:LAttack complexity, low
- An attacker who can open the device reliably triggers the bug by writing any TPM command to create a pending response, then calling pread() with a large offset; no races or special memory layout are required.
- PR:LPrivileges required, low
- Upstream tpm2-tss udev rules grant non-root users in the tss group read/write access to /dev/tpmrm0 (mode 0660), which is the standard TPM2 user-space interface on laptops and servers with TPM hardware.
- UI:NUser interaction, none
- No victim interaction is required; the attacker opens the TPM device, submits a command, and issues the malicious pread() themselves without relying on another user to mount, click, or configure anything.
- S:UScope, unchanged
- The vulnerability corrupts kernel heap memory in the TPM driver on the same host; it does not by itself cross a VM, container, or IOMMU security boundary to affect a different trust domain.
- C:HConfidentiality impact, high
- Unchecked pread offsets cause copy_to_user() to read beyond the 4096-byte data_buffer into adjacent kmalloc slab memory (including tpm_space pointers), leaking kernel heap contents to userspace.
- I:HIntegrity impact, high
- A successful out-of-bounds pread also executes memset() past data_buffer, zeroing adjacent heap objects such as tpm_space session/context pointers and enabling further memory corruption or control-flow manipulation.
- A:HAvailability impact, high
- KASAN reports slab-out-of-bounds faults on both the copy_to_user read and memset write; corrupting adjacent heap structures can oops or panic the kernel during subsequent TPM operations.