Analysis Summary

A security researcher has disclosed technical details and a proof-of-concept (PoC) exploit for a high-severity Linux kernel vulnerability, identified as CVE-2023-6931 with high severity. The flaw is a heap out-of-bounds write in the Performance Events system component, which can be exploited for local privilege escalation. It arises from how the perf_event subsystem handles event groups when the PERF_FORMAT_GROUP flag is used in its read_format.

This flag enables multiple performance counters to be read simultaneously under a single leader event. However, the kernel tracks the read size with a 16-bit variable, which can overflow when too many events are grouped. As a result, the perf_read_group() function allocates an undersized buffer and then writes beyond its bounds while iterating through the event list.

The exploit uses heap spraying and netlink socket objects, strategically placing a netlink_sock object before the vulnerable buffer. By corrupting two function pointers in the socket object, the exploit bypasses Kernel Address Space Layout Randomization (KASLR) and executes a Return-Oriented Programming (ROP) chain. This grants the attacker root-level shell access. The vulnerability has been present since Linux kernel 3.16, introduced in 2014, and was only fully patched in version 6.7 with commit 382c27f4ed28.

The public release of the exploit on GitHub makes CVE-2023-6931 an immediate real-world threat, particularly in shared hosting environments, Capture-The-Flag (CTF) competitions, and other scenarios where unprivileged user access is possible. Linux users and administrators are urged to update their systems to a patched kernel version as soon as possible to protect against potential attacks exploiting this vulnerability.

Impact

• Privilege Escalation
• Buffer Overflow

Indicators of Compromise

CVE

• CVE-2023-6931

Affected Vendors

Affected Products

• Linux Kernel 5.4
• Linux Kernel 4.19
• Linux Kernel 5.10
• Linux Kernel 5.15
• Linux Kernel 6.1
• Linux Kernel 6.6

Remediation

• Refer to Linux Kernel GIT Repository for patch, upgrade or suggested workaround information.
• If updating the kernel is not immediately possible, apply backported patches provided by your Linux distribution.
• Regularly monitor and apply security updates from your distribution’s package manager.
• Restrict local user access on systems where possible to reduce the risk of local exploitation.
• Use security tools like SELinux or AppArmor to add extra layers of protection against privilege escalation.
• Monitor system logs and behavior for any suspicious activity that may indicate exploitation attempts.
• In shared or multi-user environments, consider isolating users using containers or virtual machines to limit the impact of potential exploits.
• Subscribe to Linux kernel security advisories to stay informed about newly discovered vulnerabilities and patches.