Use-after-free in Linux kernel - CVE-2026-98256

Vulnerability identifier: #VU153764

CSH Severity: Low

CVSS v4: 5.7 [CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-98256

CWE-ID: CWE-416

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to use-after-free in the Linux kernel signal-handling subsystem when handling signals during a non-leader thread's execve() operation. A local user can trigger a race between POSIX timer signal delivery and pending-signal flushing, followed by a tgkill() call that writes to freed timer memory, to cause a denial of service.

The described race requires a SIGEV_THREAD_ID timer targeting the original thread group leader, with its signal blocked and queued on that leader's pending-signal queue.

Linux kernel
Ubuntu
linux (Ubuntu package)
linux-aws (Ubuntu package)
linux-gcp (Ubuntu package)
linux-oracle (Ubuntu package)
linux-ibm (Ubuntu package)
linux-hwe-7.0 (Ubuntu package)
linux-oem-7.0 (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux (Ubuntu package) - update to 7.0.0-42.42
linux-aws (Ubuntu package) - update to 7.0.0-1016.17
linux-gcp (Ubuntu package) - update to 7.0.0-1016.18
linux-oracle (Ubuntu package) - update to 7.0.0-1015.16
linux-ibm (Ubuntu package) - update to 7.0.0-1017.17
linux-hwe-7.0 (Ubuntu package) - update to 7.0.0-42.42~24.04.1
linux-oem-7.0 (Ubuntu package) - update to 7.0.0-1017.17

• https://git.kernel.org/stable/c/621c365739828900f32a0c1cdfe5387528a62176
• https://git.kernel.org/stable/c/934bd95f1a6404dbb845951b823547abab05a649
• https://git.kernel.org/stable/c/d2710c8d938ae6a825a6463158e6e6f31eac792a

• Use-after-free in Linux kernel kernel/signal.c: __send_signal_locked() and posixtimer_send_sigqueue(); kernel/exit.c: release_task()
• Ubuntu update for linux-oem-7.0
• Ubuntu update for linux, linux-aws, linux-gcp and more