CVE-2021-47478 is a medium-severity vulnerability in the Linux kernel's ISO filesystem (isofs) implementation. The vulnerability arises from an out-of-bounds read condition in the isofs_read_inode() function when processing a corrupted ISO filesystem image. Specifically, if an attacker supplies a malformed or corrupted isofs image, the function may read data beyond the allocated buffer boundary due to insufficient validation of directory entry lengths. This can lead to unauthorized disclosure of kernel memory contents, impacting confidentiality. The flaw is categorized under CWE-125 (Out-of-bounds Read). The vulnerability requires local privileges with limited user privileges (PR:L) and does not require user interaction (UI:N). The attack vector is local (AV:L), meaning an attacker must have some level of access to the system to exploit it. The vulnerability does not affect integrity or availability but poses a confidentiality risk by potentially exposing sensitive kernel memory data. The CVSS v3.1 base score is 5.5 (medium severity), reflecting the moderate impact and limited attack vector. No known exploits are currently reported in the wild. The vulnerability was addressed by adding sanity checks on directory entry lengths before accessing the data, preventing out-of-bounds reads. The affected versions correspond to specific Linux kernel commits prior to the fix published on May 22, 2024.

For European organizations, this vulnerability primarily threatens confidentiality on Linux systems that mount or process ISO filesystem images, such as those used for software installation or media access. Attackers with local access—such as malicious insiders, compromised user accounts, or attackers leveraging other vulnerabilities to gain limited local privileges—could exploit this flaw to read sensitive kernel memory. This could lead to leakage of sensitive information, including cryptographic keys, passwords, or other protected data residing in kernel memory. While the vulnerability does not allow privilege escalation or denial of service directly, the confidentiality breach could facilitate further attacks or data exfiltration. Organizations relying heavily on Linux servers, workstations, or embedded devices that handle ISO images are at risk. The impact is more pronounced in environments with multi-user access or where untrusted users can mount or interact with ISO images. Given the local attack vector and requirement for limited privileges, remote exploitation is unlikely without prior access. However, in shared or cloud environments where multiple users have local access, the risk increases. The absence of known exploits reduces immediate risk but patching is recommended to prevent future exploitation.

1. Apply the latest Linux kernel updates that include the patch for CVE-2021-47478 as soon as possible to eliminate the vulnerability. 2. Restrict local user privileges to the minimum necessary, especially limiting the ability to mount or access ISO filesystem images. 3. Implement strict access controls and monitoring on systems that handle ISO images, including logging mount operations and user activities related to ISO files. 4. Use filesystem integrity and security tools to detect and prevent the use of corrupted or malicious ISO images. 5. In multi-tenant or shared environments, isolate user sessions and enforce strong separation to prevent local privilege abuse. 6. Educate system administrators and users about the risks of mounting untrusted ISO images and enforce policies to only use verified and trusted media. 7. Employ kernel security modules (e.g., SELinux, AppArmor) to restrict kernel module behaviors and access to filesystem operations where feasible. 8. Regularly audit and update Linux systems to maintain security posture against known vulnerabilities.