CVE-2025-39735 is a vulnerability identified in the Linux kernel's handling of extended attributes (xattr) within the JFS (Journaled File System) module, specifically in the function ea_get(). The issue arises during a size validation step where the size of the extended attribute list (EALIST_SIZE) is compared against an integer maximum (INT_MAX). The EALIST_SIZE can return a value (e.g., 4110417968) that exceeds the maximum positive value for a signed 32-bit integer (2,147,483,647). The code attempts to clamp the size value within a range using clamp_t(int, ea_size, 0, EALIST_SIZE), but because the upper bound is treated as a signed int, the large unsigned value overflows and wraps around to a negative integer (-184549328). This negative size is then passed to print_hex_dump(), which expects a size_t (unsigned) parameter. Due to type conversions and subsequent assignments to signed integers, the loop controlling the hex dump operation iterates an extremely large number of times (effectively 18446744073525002176 iterations). This causes out-of-bounds memory reads in hex_dump_to_buffer(), as the pointer arithmetic exceeds the actual buffer size. The vulnerability can lead to slab-out-of-bounds reads, potentially leaking kernel memory contents or causing kernel crashes (denial of service). The root cause is insufficient validation of the extended attribute list size before its use, allowing integer overflow and subsequent memory corruption. The vulnerability affects multiple Linux kernel versions identified by their commit hashes, indicating it is present in several recent kernel builds. No known exploits are currently reported in the wild, and no CVSS score has been assigned yet. The fix involves proper validation of EALIST_SIZE to ensure it does not exceed INT_MAX before usage, preventing integer overflow and out-of-bounds access.

For European organizations, this vulnerability poses a significant risk primarily to systems running vulnerable Linux kernel versions with JFS support enabled. The impact includes potential kernel memory disclosure due to out-of-bounds reads, which could leak sensitive information from kernel memory, including cryptographic keys or other sensitive data. Additionally, the out-of-bounds access can cause kernel panics or crashes, leading to denial of service conditions on critical servers or infrastructure. Organizations relying on Linux-based servers for web hosting, cloud infrastructure, or internal services could experience service disruptions or data exposure. Given the Linux kernel's widespread use in European enterprises, cloud providers, and government systems, the vulnerability could affect a broad range of sectors including finance, healthcare, telecommunications, and public administration. Although exploitation requires triggering the vulnerable code path (likely via crafted extended attributes on JFS filesystems), the complexity is moderate due to the need to manipulate filesystem metadata. However, once exploited, the consequences could be severe, especially in environments where kernel stability and confidentiality are paramount. The lack of known exploits suggests limited immediate threat, but proactive patching is critical to prevent future exploitation.

1. Immediate application of kernel patches that validate EALIST_SIZE before use is essential. Organizations should monitor Linux kernel updates and apply security patches as soon as they are released. 2. Disable or avoid using the JFS filesystem if it is not required, as this reduces the attack surface. 3. Implement strict access controls on who can create or modify extended attributes on filesystems, limiting the ability of unprivileged users to trigger the vulnerability. 4. Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to mitigate potential exploitation impact. 5. Use security monitoring tools to detect unusual kernel crashes or memory access anomalies that could indicate exploitation attempts. 6. For critical systems, consider deploying intrusion detection systems that can monitor for attempts to exploit extended attribute handling. 7. Conduct regular audits of filesystem usage and extended attribute configurations to identify and remediate risky configurations. 8. Educate system administrators about the vulnerability and the importance of timely patching and filesystem management.