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CVE-2025-71109
MIPS: ftrace: Fix memory corruption when kernel is located beyond 32 bits
Published 2026-01-14 (9 months ago) by the Linux kernel CNA. Subsystem arch/mips. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2025-71109 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixedDSA-6126-1 · 2026-02-09 · text | 6.12.69-1 | Update the kernel and reboot. DSA-6126-1 shipped the fix on 2026-02-09, in 6.12.69-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.18.3-1 | Update the kernel and reboot. Fixed in 6.18.3-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.18.3-1 | Update the kernel and reboot. Fixed in 6.18.3-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Since commit e424054000878 ("MIPS: Tracing: Reduce the overhead of dynamic Function Tracer"), the macro UASM_i_LA_mostly has been used, and this macro can generate more than 2 instructions. At the same time, the code in ftrace assumes that no more than 2 instructions can be generated, which is why it stores them in an int[2] array. However, as previously noted, the macro UASM_i_LA_mostly (and now UASM_i_LA) causes a buffer overflow when _mcount is beyond 32 bits. This leads to corruption of the variables located in the __read_mostly section. This corruption was observed because the variable __cpu_primary_thread_mask was corrupted, causing a hang very early during boot. This fix prevents the corruption by avoiding the generation of instructions if they could exceed 2 instructions in length. Fortunately, insn_la_mcount is only used if the instrumented code is located outside the kernel code section, so dynamic ftrace can still be used, albeit in a more limited scope. This is still preferable to corrupting memory and/or crashing the kernel.
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.
arch/mips/kernel/ftrace.c
- What this is
- FUNCTION HOOKS (FTRACE)MAINTAINERS section matched on arch/*/*/*ftrace* · linux-kernel@vger.kernel.org · Maintained
Check it on the machine
grep -wE 'CONFIG_FTRACE_SYSCALLS|CONFIG_FUNCTION_TRACER' /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 switches
- CONFIG_FTRACE_SYSCALLS, CONFIG_FUNCTION_TRACER
- Reads as
- all on means the file is compiled; any one off means it is not.
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
- 2026-01-14 (9 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.21%, higher than 10.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- arch/mips
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.35 | 6.12.64 | e3e33ac2eb69 |
| 2.6.35 | 6.18.3 | 7f39b9d0e86e |
| 2.6.35 | 6.19 | 36dac9a3dda1 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6126-1 | 2026-02-09 | trixie 6.12.69-1 | tracker |
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 overflow occurs only during local MIPS kernel boot-time ftrace initialization; no network, radio, or device-input handler reaches it.
- AC:LAttack complexity, low
- On an affected build with dynamic ftrace and _mcount beyond 32-bit compatibility space, the overflow occurs deterministically during every boot without a race or heap grooming.
- PR:LPrivileges required, low
- No ftrace or tracefs permission check gates the vulnerable boot path, which executes before userspace; conservatively, ordinary local access is sufficient rather than requiring real root.
- UI:NUser interaction, none
- The vulnerable instruction generation happens automatically during normal kernel boot without requiring a victim to enable tracing, mount tracefs, or open a file.
- S:UScope, unchanged
- The corruption affects the same kernel security authority and does not cross a VM, IOMMU, or sandbox boundary.
- C:NConfidentiality impact, none
- The bounded overwrite emits deterministic MIPS instruction words and provides no identified memory-read primitive or path for returning corrupted memory to an attacker.
- I:HIntegrity impact, high
- Up to several instructions are written beyond the two-word array into adjacent kernel globals, constituting an out-of-bounds kernel write capable of corrupting security-critical state.
- A:HAvailability impact, high
- Corruption of __cpu_primary_thread_mask was observed to hang the kernel very early during boot, preventing affected servers, embedded controllers, or automotive systems from becoming operational.