CVE-2025-38682 in Linux
Summary
by MITRE • 09/04/2025
In the Linux kernel, the following vulnerability has been resolved:
i2c: core: Fix double-free of fwnode in i2c_unregister_device()
Before commit df6d7277e552 ("i2c: core: Do not dereference fwnode in struct device"), i2c_unregister_device() only called fwnode_handle_put() on of_node-s in the form of calling of_node_put(client->dev.of_node).
But after this commit the i2c_client's fwnode now unconditionally gets fwnode_handle_put() on it.
When the i2c_client has no primary (ACPI / OF) fwnode but it does have a software fwnode, the software-node will be the primary node and fwnode_handle_put() will put() it.
But for the software fwnode device_remove_software_node() will also put() it leading to a double free:
[ 82.665598] ------------[ cut here ]------------
[ 82.665609] refcount_t: underflow; use-after-free.
[ 82.665808] WARNING: CPU: 3 PID: 1502 at lib/refcount.c:28 refcount_warn_saturate+0xba/0x11
... [ 82.666830] RIP: 0010:refcount_warn_saturate+0xba/0x110
... [ 82.666962] <TASK>
[ 82.666971] i2c_unregister_device+0x60/0x90
Fix this by not calling fwnode_handle_put() when the primary fwnode is a software-node.
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Analysis
by VulDB Data Team • 02/10/2026
The vulnerability CVE-2025-38682 represents a critical double-free condition in the Linux kernel's I2C subsystem that arises from improper firmware node handling during device deregistration. This flaw specifically affects the i2c_unregister_device() function within the I2C core driver, where the kernel fails to properly distinguish between different types of firmware nodes when performing reference counting operations. The issue stems from a change introduced in commit df6d7277e552 that modified how firmware nodes are processed during I2C device cleanup, creating a scenario where software-defined firmware nodes can be freed twice, leading to memory corruption and potential system instability.
The technical root cause of this vulnerability lies in the improper handling of firmware node references when an I2C client device has a software firmware node as its primary node. In the affected kernel versions, the i2c_unregister_device() function unconditionally calls fwnode_handle_put() on all firmware nodes associated with the device, regardless of their type or origin. When a device possesses both a software firmware node and a primary firmware node, the system attempts to decrement the reference count of the same node twice. The first call occurs through the standard fwnode_handle_put() mechanism, while the second occurs through device_remove_software_node() which also decrements the reference count of the software firmware node, resulting in a double-free scenario that triggers kernel memory management warnings and can lead to system crashes.
This vulnerability directly relates to CWE-415, which describes double free conditions in software systems, and represents a classic example of improper resource management in kernel space. The operational impact of this flaw extends beyond simple system crashes, as it can enable privilege escalation attacks and potentially allow malicious actors to execute arbitrary code within the kernel context. The vulnerability manifests as a refcount_t underflow error, which is a clear indicator of memory corruption, and the kernel's panic response demonstrates the severity of the underlying memory management issue. Attackers could exploit this weakness by creating I2C devices with specific firmware node configurations, potentially leading to complete system compromise.
Mitigation strategies for CVE-2025-38682 require immediate kernel updates to versions containing the fix that prevents calling fwnode_handle_put() when the primary firmware node is a software node. System administrators should prioritize patching affected systems, particularly those running embedded Linux systems or devices that rely heavily on I2C communication protocols. Additional defensive measures include implementing kernel lockdown mechanisms and monitoring for unusual memory management patterns, though the most effective solution remains the application of the official kernel patch. The fix implemented addresses the specific condition where software firmware nodes should not undergo the standard fwnode_handle_put() operation, thereby preventing the double-free scenario while maintaining proper reference counting for all other firmware node types. This vulnerability also aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', as the memory corruption could potentially be leveraged to gain elevated privileges within the kernel space.