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CVE-2026-98260
exec: Cleanup POSIX timers right after de_thread()
Published 2026-10-06 (13 days ago) by the Linux kernel CNA. Subsystem fs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-98260 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 | fixedDLA-4841-1 · 2026-10-17 · text | 6.1.190-1 | Update the kernel and reboot. DLA-4841-1 shipped the fix on 2026-10-17, in 6.1.190-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6568-1 · 2026-10-16 · text | 6.12.113-1 | Update the kernel and reboot. DSA-6568-1 shipped the fix on 2026-10-16, in 6.12.113-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.2.8-1 | Update the kernel and reboot. Fixed in 7.2.8-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
A per-thread CPU timer holds a reference to the PID of the thread it is attached to and, while it is armed, its node is queued in that thread's posix_cputimers. The task is looked up by that PID. When a non-leader thread exec()s, de_thread() changes which task owns that PID. pid_task(timer->it.cpu.pid, PIDTYPE_PID) then returns NULL, but the node is still queued on tsk, which is alive. timer_lock_sighand() takes a failed lookup to mean that the node is already dequeued, so it has nothing to undo. begin_new_exec() calls posix_cpu_timers_exit(me) right after exec_task_namespaces() and that removes the leftover node, so the state normally stays invisible. But bprm->point_of_no_return is set before de_thread(), so if unshare_files(), set_mm_exe_file(), exec_mmap() or exec_task_namespaces() fails, the task dies before it gets there. exit_itimers() then frees the k_itimer while its node is still queued, and reaping tsk later erases that freed node from the rbtree. In short: the non-leader thread B the parent timer_create(CLOCK_THREAD_CPUTIME_ID) timer_settime() arm_timer() // the node is queued on B execve() de_thread(B) exchange_tids(B, leader) // B's PID now belongs to the leader release_task(leader) __exit_signal(leader) posix_cpu_timers_exit(leader) // cleans leader's queue, not B's __unhash_process(leader) // that PID has no task anymore exec_mmap() mmap_read_lock_killable(old_mm) kill(B, SIGKILL) // -EINTR get_signal() do_exit() exit_itimers() posix_timer_delete() posix_cpu_timer_del() posix_timer_unhash_and_free() // freed while still queued wait4() release_task(B) posix_cpu_timers_exit(B) cleanup_timerqueue() timerqueue_del() // use-after-free Move the POSIX timer cleanup right after de_thread() before any of the later failure conditions brings the task into do_exit(). [ tglx: Move the cleanup right after de_thread() ]
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.
fs/exec.c
- What this is
- EXEC & BINFMT API, ELFMAINTAINERS section matched on fs/exec.c · linux-mm@kvack.org · Supported
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
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 Debian linux-config packages
Signals
- Published
- 2026-10-06 (13 days 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
- 0.13%, higher than 2.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.7 | 6.6.158 | 6f1977cea3e8 |
| 5.7 | 6.12.112 | d9ae467e617c |
| 5.7 | 6.18.54 | 75aa08b93c65 |
| 5.7 | 7.2.8 | d602877baf36 |
| 5.7 | 7.3 | acb03d388181 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4841-1 | 2026-10-17 | bookworm 6.1.190-1 | tracker |
| DSA-6568-1 | 2026-10-16 | trixie 6.12.113-1 | 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 bug needs local syscalls: timer_create(CLOCK_THREAD_CPUTIME_ID) and timer_settime() on a non-leader thread, then execve(). That thread's exec must fail after de_thread() in begin_new_exec() (e.g. exec_mmap() returning -EINTR on SIGKILL). No remote protocol carries any of this input.
- AC:LAttack complexity, low
- The attacker controls both sides of the race. Their own parent sends SIGKILL while exec_mmap() waits on down_write_killable(exec_update_lock) or mmap_read_lock_killable(old_mm), and they can create that lock contention with their own CLONE_VM or /proc readers. No condition outside their control is needed.
- PR:LPrivileges required, low
- Arming a thread CPU timer, calling execve and signalling one's own child are all available to any unprivileged user, with no capability checks on this path. A local unprivileged account is enough.
- UI:NUser interaction, none
- The attacker's own processes perform every step (timer arm, execve from a non-leader thread, SIGKILL, wait4 reap), so no victim action is needed.
- S:UScope, unchanged
- The memory corruption is inside the kernel that the attacker's process runs on. The outcome is a normal local privilege escalation, with no VM or sandbox boundary crossed.
- C:HConfidentiality impact, high
- exit_itimers() frees the k_itimer while its cpu_timer node is still linked in the task's posix_cputimers rbtree. The freed slab object can be reclaimed with attacker-sprayed data, giving a use-after-free that can be turned into kernel memory disclosure.
- I:HIntegrity impact, high
- When release_task() reaps the task, posix_cpu_timers_exit() -> cleanup_timerqueue() -> timerqueue_del() calls rb_erase on the freed node and rewrites rbtree pointers in reclaimed memory. That is a use-after-free write which can be used for privilege escalation.
- A:HAvailability impact, high
- The rbtree erase on freed memory corrupts kernel data and can oops or panic the kernel. Any unprivileged user can repeat it at will.