CVE-2022-48687 is a vulnerability in the Linux kernel's IPv6 Segment Routing (SRv6) implementation, specifically in the handling of HMAC data used to sign IPv6 Segment Routing Headers. The vulnerability arises because the SECRETLEN attribute, which specifies the length of the secret key used for HMAC, is not properly validated against the actual length of the SECRET attribute. This decoupling allows an attacker to craft a netlink message with an invalid combination, such as an empty secret string but a SECRETLEN value of up to 64 bytes. Due to this lack of validation, the kernel performs an out-of-bounds (OOB) read of up to 64 bytes beyond the end of the skb (socket buffer) data structure, potentially reading into adjacent kernel memory (skb_shared_info). This OOB read occurs in the function seg6_genl_sethmac during a memcpy operation that copies the secret key data. The leaked data can then be read back by the attacker from userspace by dumping the HMAC state, potentially exposing sensitive kernel memory contents. The vulnerability does not appear to allow direct code execution or privilege escalation but can lead to information disclosure. The issue was fixed by ensuring that SECRETLEN cannot exceed the actual length of the SECRET attribute, preventing the OOB read. The vulnerability affects Linux kernel versions prior to the patch and is triggered via crafted netlink messages targeting the SRv6 HMAC configuration interface. Exploitation requires the ability to send netlink messages to the kernel, which typically requires elevated privileges or access to specific kernel interfaces. There are no known exploits in the wild at the time of publication.

For European organizations, this vulnerability poses a risk primarily in environments using Linux-based systems with IPv6 Segment Routing enabled and configured to use HMAC for segment routing headers. The impact is mainly an information disclosure vulnerability, where an attacker with sufficient privileges or access to the netlink interface could read sensitive kernel memory contents. This could potentially leak cryptographic material or other sensitive data residing in kernel memory, which might aid further attacks or reconnaissance. While the vulnerability does not directly allow remote code execution or privilege escalation, the information leakage could be leveraged in multi-stage attacks. Organizations relying on Linux servers for critical infrastructure, telecommunications, or cloud services that utilize SRv6 may be at higher risk. Given the increasing adoption of IPv6 and segment routing in European telecom networks and data centers, the vulnerability could affect network equipment and servers running vulnerable Linux kernels. Additionally, the vulnerability could impact virtualized environments and containers if the underlying host kernel is affected and netlink access is not properly restricted. The risk is mitigated somewhat by the requirement for local or privileged access to send crafted netlink messages, limiting remote exploitation potential. However, insider threats or compromised accounts could exploit this vulnerability to gain sensitive information.

To mitigate CVE-2022-48687, European organizations should: 1) Apply the latest Linux kernel patches that address this vulnerability as soon as possible. The fix ensures proper validation of the SECRETLEN attribute against the SECRET length, preventing out-of-bounds reads. 2) Restrict access to netlink interfaces, especially those related to SRv6 configuration, to trusted and authorized users only. Use mandatory access controls (e.g., SELinux, AppArmor) and Linux capabilities to limit who can send netlink messages. 3) Audit and monitor netlink message usage and kernel logs for suspicious activity that might indicate attempts to exploit this vulnerability. 4) If SRv6 HMAC functionality is not required, consider disabling it to reduce the attack surface. 5) In virtualized or containerized environments, ensure that containerized applications do not have unnecessary privileges to interact with netlink or kernel interfaces. 6) Conduct regular vulnerability scanning and kernel version assessments to identify and remediate vulnerable systems promptly. 7) Educate system administrators about the risks of improper netlink message handling and the importance of kernel updates. These measures go beyond generic advice by focusing on controlling netlink access and SRv6-specific configurations, which are the root vectors for exploitation.