CVE-2024-35821 is a high-severity vulnerability in the Linux kernel affecting the UBIFS (UBI File System) component. The issue arises from improper handling of the page cache's 'uptodate' flag during write operations. Specifically, the vulnerability occurs because the kernel sets the 'PageUptodate' flag on a freshly allocated page before the new data has been fully written to it. Since page cache reads are lockless, this premature flag setting can allow a concurrent reader to access stale or old data instead of the updated content. The flaw is rooted in the sequence of operations within the ubifs_write_end() function, where the flag should only be set after the new data has been copied into the page. This vulnerability is classified under CWE-772 (Missing Release of Resource after Effective Lifetime), indicating a resource state management issue. The CVSS v3.1 base score is 7.5, reflecting a high severity with network attack vector (AV:N), low attack complexity (AC:L), no privileges required (PR:N), no user interaction (UI:N), unchanged scope (S:U), no confidentiality impact (C:N), high integrity impact (I:H), and no availability impact (A:N). The vulnerability does not require authentication or user interaction and can be exploited remotely. Although no known exploits are currently reported in the wild, the potential for data integrity compromise is significant. The fix involves moving the SetPageUptodate call to the correct location after data copying in ubifs_write_end(), ensuring readers do not see stale data. This vulnerability affects Linux kernel versions identified by the given commit hashes, implying a range of recent kernel builds prior to the patch date of May 17, 2024.

For European organizations, this vulnerability poses a risk primarily to systems running Linux kernels with UBIFS support, commonly used in embedded devices, IoT equipment, and specialized storage solutions. The main impact is on data integrity, where concurrent reads might retrieve outdated or incorrect data, potentially leading to application errors, data corruption, or incorrect decision-making based on stale information. This can be critical in sectors such as finance, healthcare, manufacturing, and critical infrastructure where data accuracy is paramount. Although confidentiality and availability are not directly affected, the integrity breach could undermine trust in system outputs and cause cascading operational issues. Since the vulnerability can be exploited remotely without authentication, exposed Linux systems with UBIFS could be targeted by attackers to manipulate data silently. European organizations relying on embedded Linux devices in industrial control systems or telecommunications infrastructure may face increased risk. The absence of known exploits reduces immediate threat but does not eliminate the urgency of patching, especially given the ease of exploitation and high impact on integrity.

European organizations should prioritize updating Linux kernels to versions that include the patch for CVE-2024-35821. Specifically, ensure that all devices and systems using UBIFS are running the latest stable kernel releases post-May 2024. For embedded and IoT devices where kernel updates are challenging, vendors should be engaged to provide firmware updates or mitigations. Network segmentation and firewall rules should be applied to limit exposure of vulnerable devices to untrusted networks, reducing the attack surface. Monitoring and logging of file system operations on critical systems can help detect anomalous behavior indicative of exploitation attempts. Additionally, organizations should review their data integrity verification processes and implement application-level checksums or validation to detect stale or corrupted data. For development teams, auditing code that interacts with UBIFS and page cache mechanisms can help identify similar race conditions or improper synchronization issues. Finally, maintain an inventory of Linux-based devices with UBIFS to ensure comprehensive coverage of patching efforts.