Uncontrolled Recursion in Linux kernel - CVE-2026-63983

Vulnerability identifier: #VU138667

CSH Severity: Low

CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63983

CWE-ID: CWE-674

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 uncontrolled recursion in netem packet duplication handling in the netem qdisc when processing duplicated packets through a qdisc tree containing another netem instance. A local user can trigger packet duplication to cause a denial of service.

Exploitation can exhaust stack or memory when packet duplication is enabled and duplicated packets are re-enqueued through another netem in the tree.

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

• https://git.kernel.org/stable/c/1a298a514ce766c6d0c232991a390fec67af81ad
• https://git.kernel.org/stable/c/9552b11e3edabc97cfcd9f29103d5afbce7ae183
• https://git.kernel.org/stable/c/cfb2616042767ab31260d4f39190c381bec8b12e

• Uncontrolled Recursion in Linux kernel sched
• Ubuntu update for linux-ibm
• Ubuntu update for linux-azure
• Ubuntu update for linux-aws
• Ubuntu update for linux-nvidia-bos
• Ubuntu update for linux-nvidia