CVE-2023-3776 in Linux
Summary
by MITRE • 07/22/2023
A use-after-free vulnerability in the Linux kernel's net/sched: cls_fw component can be exploited to achieve local privilege escalation.
If tcf_change_indev() fails, fw_set_parms() will immediately return an error after incrementing or decrementing the reference counter in tcf_bind_filter(). If an attacker can control the reference counter and set it to zero, they can cause the reference to be freed, leading to a use-after-free vulnerability.
We recommend upgrading past commit 0323bce598eea038714f941ce2b22541c46d488f.
If you want to get the best quality for vulnerability data then you always have to consider VulDB.
Analysis
by VulDB Data Team • 08/22/2024
The vulnerability described in CVE-2023-3776 represents a critical use-after-free flaw within the Linux kernel's traffic control subsystem, specifically in the net/sched/cls_fw component. This issue arises from improper handling of reference counting mechanisms during filter parameter updates, creating a pathway for local privilege escalation attacks. The vulnerability is particularly concerning because it exists within kernel space code that manages network packet filtering and classification, making it accessible to any local user who can execute malicious code with sufficient privileges to manipulate kernel data structures. The flaw stems from a race condition in the tcf_change_indev() function where error handling does not properly account for reference counter states, allowing attackers to manipulate object lifecycles through controlled reference modifications.
The technical implementation of this vulnerability involves a specific sequence of operations that leads to memory corruption. When fw_set_parms() encounters an error condition from tcf_change_indev(), it immediately returns without properly managing the reference counter that was modified by tcf_bind_filter(). This function performs increment or decrement operations on reference counters, but when these operations are followed by an early return due to error conditions, the reference counter can reach zero while the object remains referenced elsewhere in the system. This creates a scenario where subsequent operations may attempt to access memory that has already been freed, resulting in a use-after-free condition that can be exploited to execute arbitrary code with kernel privileges. The vulnerability is classified under CWE-416 as a Use After Free condition, and specifically relates to improper handling of reference counting in kernel memory management.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with complete control over the target system. Local privilege escalation through kernel-level use-after-free vulnerabilities enables attackers to bypass traditional user-space security controls and gain root access to the compromised system. This can lead to persistent backdoor installation, data exfiltration, system monitoring, and further lateral movement within network environments. The attack vector requires local access and execution capabilities, but once exploited, the consequences are severe enough to warrant immediate remediation across all affected systems. The vulnerability affects Linux kernel versions that include the problematic code path, particularly those incorporating the commit referenced in the advisory, making it a widespread concern for system administrators managing kernel-based infrastructure.
Mitigation strategies for CVE-2023-3776 focus primarily on applying the recommended kernel upgrade that addresses the specific reference counting issue in the cls_fw component. System administrators should prioritize patching their kernel installations to versions that include the fix referenced in commit 0323bce598eea038714f941ce2b22541c46d488f, which properly handles the reference counter state management during error conditions. Additional defensive measures include implementing kernel lockdown mechanisms, disabling unnecessary network filtering features when not required, and monitoring for suspicious kernel-level activities that might indicate exploitation attempts. Organizations should also consider implementing runtime protections such as kernel module signing, control flow integrity checks, and memory protection mechanisms that can detect or prevent exploitation attempts. From an ATT&CK perspective, this vulnerability maps to T1068 (Local Privilege Escalation) and T1547.001 (Registry Run Keys / Startup Folder), as successful exploitation would enable attackers to establish persistent access and potentially escalate privileges to root level. The vulnerability demonstrates the importance of proper memory management and reference counting in kernel space code, highlighting the critical need for thorough testing and validation of error handling paths in security-sensitive subsystems.