Out-of-bounds write in Linux kernel - CVE-2026-98621

Vulnerability identifier: #VU156931

CSH Severity: Medium

CVSS v4: 8.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-98621

CWE-ID: CWE-787

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to corrupt kernel memory and potentially cause a denial of service.

The vulnerability exists due to an integer underflow leading to an out-of-bounds write in the Linux kernel's GUE REMCSUM processing when the checksum field offset is less than the checksum start offset. A remote attacker can send a specially crafted GUE packet to underflow the checksum offset stored in skb->csum_offset and trigger a two-byte write approximately 64 KiB beyond the destination buffer if the forwarded packet retains CHECKSUM_PARTIAL and reaches a NETIF_F_HW_CSUM driver that trusts this metadata.

Linux kernel
Ubuntu
linux-nvidia-tegra (Ubuntu package)
linux-nvidia-tegra-igx (Ubuntu package)
linux-nvidia-tegra-5.15 (Ubuntu package)
linux (Ubuntu package)
linux-gcp (Ubuntu package)
linux-oracle (Ubuntu package)
linux-aws (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-nvidia-tegra (Ubuntu package) - update to 5.15.0-1070.72
linux-nvidia-tegra-igx (Ubuntu package) - update to 5.15.0-1059.59
linux-nvidia-tegra-5.15 (Ubuntu package) - update to 5.15.0-1070.72~20.04.1
linux (Ubuntu package) - update to 7.0.0-42.42
linux-gcp (Ubuntu package) - update to 7.0.0-1016.18
linux-oracle (Ubuntu package) - update to 7.0.0-1015.16
linux-aws (Ubuntu package) - update to 7.0.0-1016.17
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/1d664be4ca49d1696e85239236f4988dfc4653c3
• https://git.kernel.org/stable/c/1eeec0c51fd5598da44080ed96bbd9880021c28b
• https://git.kernel.org/stable/c/2566866fc30965d915d0b52b5c3323b362619f0e
• https://git.kernel.org/stable/c/40aeafbcbc7bc4018e8f74bbbb4d29ed8846f57f
• https://git.kernel.org/stable/c/43efb1f997e976f386aa89716f55870cd2cff9ad
• https://git.kernel.org/stable/c/4b9bc21b2396c396d88dd909caaf73d5be6ff593
• https://git.kernel.org/stable/c/97f907203321eee2cc9132d5c9eb47698fb41d35
• https://git.kernel.org/stable/c/c20f755338ca234e523dfc943719f194dfc1f903

• Out-of-bounds write in Linux kernel net
• Ubuntu update for linux-oem-7.0
• Ubuntu update for linux, linux-aws, linux-gcp and more
• Ubuntu update for linux-nvidia-tegra, linux-nvidia-tegra-5.15, linux-nvidia-tegra-igx
• Ubuntu update for linux, linux-aws, linux-aws-5.15 and more