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Linux Distros Unpatched Vulnerability : CVE-2026-72166

critical Nessus Plugin ID 335631

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Synopsis

The Linux/Unix host has one or more packages installed with a vulnerability that the vendor indicates will not be patched.

Description

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

 - net/9p: fix infinite loop in p9_client_rpc on fatal signal When p9_client_rpc() is called with type P9_TFLUSH and the transport has no peer (e.g. fd transport backed by pipes with no 9p server), a fatal signal causes an infinite loop: again: err = io_wait_event_killable(req->wq, ...) /* SIGKILL wakes the task, returns -ERESTARTSYS */ if (err == -ERESTARTSYS && c->status == Connected && type == P9_TFLUSH) { sigpending = 1; clear_thread_flag(TIF_SIGPENDING); goto again; } clear_thread_flag() clears TIF_SIGPENDING before jumping back to io_wait_event_killable(). signal_pending_state() checks TIF_SIGPENDING, finds it zero, and the task goes to sleep again. The task can only wake on the next signal delivery that calls signal_wake_up() and sets TIF_SIGPENDING again. When that happens the loop repeats, clears TIF_SIGPENDING, and sleeps again indefinitely. This is triggered in practice by coredump_wait(): when a thread in a multi- threaded process causes a coredump (e.g. via SIGSYS from Syscall User Dispatch), coredump_wait() sends SIGKILL to all other threads and waits for them to call mm_release(). If one of those threads is blocked in p9_client_rpc() over an fd transport with no peer, it enters the P9_TFLUSH loop and never calls mm_release(), so coredump_wait() stalls forever: INFO: task syz.0.18:676 blocked for more than 143 seconds. Not tainted 6.12.77+ #1 task:syz.0.18 state:D stack:27600 pid:676 tgid:673 ppid:630 flags:0x00000004 Call Trace: <TASK> context_switch kernel/sched/core.c:5344 [inline]
 __schedule+0xcb4/0x5d50 kernel/sched/core.c:6724 __schedule_loop kernel/sched/core.c:6801 [inline] schedule+0xe5/0x350 kernel/sched/core.c:6816 schedule_timeout+0x253/0x290 kernel/time/timer.c:2593 do_wait_for_common kernel/sched/completion.c:95 [inline] __wait_for_common+0x409/0x600 kernel/sched/completion.c:116 wait_for_common kernel/sched/completion.c:127 [inline] wait_for_completion_state+0x1d/0x40 kernel/sched/completion.c:264 coredump_wait fs/coredump.c:448 [inline] do_coredump+0x854/0x4350 fs/coredump.c:629 get_signal+0x1425/0x2730 kernel/signal.c:2903 arch_do_signal_or_restart+0x81/0x880 arch/x86/kernel/signal.c:337 exit_to_user_mode_loop kernel/entry/common.c:111 [inline] exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
 __syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline] syscall_exit_to_user_mode+0xf9/0x160 kernel/entry/common.c:218 do_syscall_64+0x102/0x220 arch/x86/entry/common.c:84 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK> Fix: check fatal_signal_pending() before clearing TIF_SIGPENDING in the P9_TFLUSH retry loop. At that point TIF_SIGPENDING is still set, so fatal_signal_pending() works correctly. If a fatal signal is pending, jump to recalc_sigpending to restore TIF_SIGPENDING and return -ERESTARTSYS to the caller. The same defect is present in stable kernels back to 5.4. On those kernels the infinite loop is broken earlier by a second SIGKILL from the parent process (e.g. kill_and_wait() retrying after a timeout), resulting in a zombie process and a shutdown delay rather than a permanent D-state hang, but the underlying flaw is the same. Found by Linux Verification Center (linuxtesting.org) with Syzkaller. (CVE-2026-72166)

Note that Nessus relies on the presence of the package as reported by the vendor.

Solution

There is no known solution at this time.

See Also

https://security-tracker.debian.org/tracker/CVE-2026-72166

Plugin Details

Severity: Critical

ID: 335631

File Name: unpatched_CVE_2026_72166.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Misc.

Published: 8/15/2026

Updated: 8/15/2026

Supported Sensors: Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 5

Percentile: 93.8

CVSS v2

Risk Factor: High

Base Score: 7.5

Temporal Score: 6.4

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS Score Source: CVE-2026-72166

CVSS v3

Risk Factor: Critical

Base Score: 9.8

Temporal Score: 9

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Temporal Vector: CVSS:3.0/E:U/RL:U/RC:C

Vulnerability Information

CPE: cpe:/o:debian:debian_linux:11.0, p-cpe:/a:debian:debian_linux:linux

Required KB Items: Host/local_checks_enabled, Host/cpu, global_settings/vendor_unpatched, Host/OS/identifier

Exploit Ease: No known exploits are available

Vulnerability Publication Date: 8/15/2026

Reference Information

CVE: CVE-2026-72166