CVE-2026-100079: 
Linux Kernel vulnerability analysis and mitigation

CVE-2026-100079 is a resource leak vulnerability in the Linux kernel's USB Type-C UCSI (USB Connector System Software Interface) subsystem, specifically in the handling of debugfs entries during device teardown. The flaw arises because ucsi_register() creates per-instance debugfs entries that are not cleaned up by ucsi_unregister(), persisting until ucsi_destroy() is called. This causes conflicts when drivers such as ucsi_glink attempt to re-register the same UCSI instance across remoteproc restarts, resulting in a denial-of-service condition. Affected Linux kernel versions include 6.6.x before 6.6.157, 6.7–6.12.x before 6.12.110, 6.13–6.18.x before 6.18.52, and 6.19–7.2.x before 7.2.6. It carries a CVSS v3.1 base score of 5.5 (Medium) (GitHub Advisory, Feedly).

The root cause is classified as CWE-772 (Missing Release of Resource after Effective Lifetime): debugfs directory entries allocated during ucsi_register() are not freed during ucsi_unregister(), only during the later ucsi_destroy() call. When a driver like ucsi_glink triggers a remoteproc restart cycle — calling ucsi_unregister() followed by ucsi_register() on the same instance — the kernel attempts to create a debugfs directory (e.g., pmic_glink.ucsi.0) that already exists, logging the error debugfs: 'pmic_glink.ucsi.0' already exists in 'ucsi'. The fix moves debugfs cleanup into ucsi_unregister() and nullifies the ucsi->debugfs pointer post-free to make repeated unregister paths safe (GitHub Advisory, Feedly). Exploitation requires local access with driver-level or root privileges.

Successful exploitation results in a denial-of-service condition affecting USB Type-C functionality on the impacted system. A local privileged user can trigger repeated unregister/register cycles of UCSI instances, causing debugfs entry conflicts that prevent proper re-registration and disrupt USB Type-C port management during device restart scenarios. There is no confidentiality or integrity impact; the vulnerability is limited to availability (CVSS availability impact: High, local attack vector) (Feedly, GitHub Advisory).

There is no public proof-of-concept exploit and no evidence of in-the-wild exploitation as of the time of this report (Feedly). The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. The EPSS score is approximately 0.00156 (~0.16%), indicating a very low probability of exploitation in the near term. Exploitation requires local access with elevated privileges, significantly limiting the attack surface.

• Logs: Kernel log messages containing debugfs: 'pmic_glink.ucsi.0' already exists in 'ucsi' (or similar UCSI instance names), indicating a failed debugfs directory creation during re-registration.
• System Behavior: USB Type-C ports becoming unresponsive or failing to re-initialize after a remoteproc or driver restart cycle on systems using ucsi_glink or similar UCSI drivers.
• Kernel Messages: Repeated dmesg entries referencing UCSI registration failures or debugfs conflicts following device or subsystem restarts.

Update the Linux kernel to a patched version that properly unregisters debugfs entries as part of ucsi_unregister() and clears the ucsi->debugfs pointer after freeing it. Fixed versions are: 6.6.157, 6.12.110, 6.18.52, 7.2.6, and 7.3-rc1 (upstream). Patches are available via the Linux stable kernel tree (GitHub Advisory, Microsoft Advisory). No configuration-based workaround is documented; upgrading to a patched kernel version is the recommended remediation. Distribution-specific updates (e.g., Debian, Ubuntu, RHEL) should be applied as they become available.

The vulnerability was covered in a Linux security roundup discussing CVEs affecting Debian and Ubuntu kernels, noting it as part of a broader batch of kernel fixes (Linux Compatible). Cybersecurity news outlets reported on Debian patching over 1,300 kernel flaws in a major update that included this CVE (CyberSecurityNews). Community reaction has been minimal given the low severity and limited exploitability of the issue.