Technical impact
A defect in the Linux kernel’s Generic Receive Offload (GRO) module causes the UDP checksum calculation to use an incorrect network offset when certain network interfaces set an encapsulation flag during offloading. The resulting checksum computation errors prevent packets from passing later validation steps, potentially leading to dropped or rejected traffic. This error can disrupt network communication for affected hosts, representing a modest Denial of Service risk. The weakness arises from improper handling of the encapsulation flag and incorrect offset usage, which aligns with known checksum calculation flaws in networking code.
Affected Systems
All Linux kernel builds that employ the Ethernet GRO path and support UDP checksum offloading are affected. The vulnerability applies to standard distribution kernels and any custom kernel configurations that enable GRO, including those using NICs that set the encapsulation flag or the tun/virtual Ethernet drivers that inject GSO packets. No specific version range is documented, but the fix has been merged into the kernel trunk and will be propagated through subsequent kernel releases. Systems should verify whether they are running a kernel version that contains the patch committing this fix.
Risk and Exploitability
The CVSS score of 5.5 indicates moderate severity, and the EPSS score of less than 1% denotes a low likelihood of current exploitation. The vulnerability is not listed in the CISA KEV catalog. Exploitation would require an attacker to deliver specially crafted UDP traffic or to manipulate NIC offloading behavior to trigger the incorrect checksum path. Such attacks are feasible over the network, but for most environments the probability of successful exploitation remains low given the minimal impact beyond packet loss or service interruption.
Ubuntu USN