CVE-2022-48689 is a medium severity vulnerability in the Linux kernel affecting the TCP zerocopy implementation. The issue arises from improper handling of the pfmemalloc page status in TCP zerocopy paths. Specifically, the kernel code incorrectly uses the page_is_pfmemalloc() function to check the pfmemalloc status of pages involved in TCP zerocopy operations. This function is intended to detect pages allocated under memory pressure conditions to avoid deadlocks, but its use in this context is inappropriate because pages coming from user space or other layers do not reliably reflect pfmemalloc status. This misuse can lead to false positives and unnecessary CPU cycles, but more critically, it introduces a data race condition as reported by Kernel Concurrency Sanitizer (KCSAN). The race condition occurs due to concurrent access and modification of linked list pointers in the Linux memory management subsystem, particularly involving the lru.next field in struct page, which was changed in a recent kernel commit to include a signature bit. The race can cause inconsistent or corrupted memory state during TCP sendpage operations, potentially leading to system instability or crashes. The vulnerability was identified through syzbot fuzzing and KCSAN reports and has been addressed by removing the pfmemalloc check in the TCP zerocopy path and introducing a prerequisite patch (__skb_fill_page_desc_noacc) to stabilize page descriptor handling. The vulnerability affects kernel versions including and after commit c07aea3ef4d4, but backporting to older kernels is not deemed necessary. Exploitation requires local privileges with low complexity, no user interaction, and can impact confidentiality, integrity, and availability to a limited extent, reflected in a CVSS score of 5.3 (medium severity). No known exploits are currently reported in the wild.

For European organizations, this vulnerability primarily poses a risk to servers and infrastructure running vulnerable Linux kernel versions, especially those handling high-performance networking workloads using TCP zerocopy for efficient data transfer. Potential impacts include system crashes or instability due to memory corruption, which can lead to denial of service conditions. While direct data leakage or privilege escalation is not explicitly reported, the data race and memory corruption could be leveraged in complex attack chains. Organizations relying on Linux-based servers for critical services such as web hosting, cloud infrastructure, or telecommunications could experience service disruptions. Given the medium severity and local privilege requirement, the threat is more significant for environments where untrusted users or processes have local access, such as multi-tenant cloud platforms or shared hosting providers. The absence of known exploits reduces immediate risk but patching is important to prevent future exploitation. The vulnerability also affects kernel versions commonly used in enterprise Linux distributions, which are widespread across Europe.

European organizations should prioritize updating Linux kernel versions to those including the patch that removes the pfmemalloc check in TCP zerocopy paths and introduces __skb_fill_page_desc_noacc. Specifically, kernel versions incorporating commit 84ce071e38a6 and later should be deployed. For environments where immediate kernel upgrades are challenging, organizations should restrict local access to trusted users only, minimizing the risk of local exploitation. Monitoring kernel logs for anomalies related to TCP sendpage or memory management errors can help detect exploitation attempts. Additionally, organizations should review and harden container and virtualization environments to limit local privilege escalation vectors. Network segmentation and strict access controls can reduce exposure of vulnerable systems. Finally, coordinating with Linux distribution vendors to receive timely security updates and backports is critical to maintain secure kernel versions.