CVE-2025-40057 in Linux
Summary
by MITRE • 10/28/2025
In the Linux kernel, the following vulnerability has been resolved:
ptp: Add a upper bound on max_vclocks
syzbot reported WARNING in max_vclocks_store.
This occurs when the argument max is too large for kcalloc to handle.
Extend the guard to guard against values that are too large for kcalloc
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Analysis
by VulDB Data Team • 05/20/2026
The vulnerability CVE-2025-40057 represents a critical buffer overflow condition within the Linux kernel's Precision Time Protocol (PTP) subsystem that arises from inadequate input validation during the configuration of virtual clocks. This issue manifests when the system attempts to process a maximum virtual clocks value that exceeds the capacity limits of the kernel's memory allocation functions. The flaw specifically occurs in the max_vclocks_store function where the kernel fails to properly validate the upper bounds of user-supplied parameters before attempting to allocate memory resources. The vulnerability stems from the absence of proper boundary checking mechanisms that would prevent the kcalloc function from receiving arguments that exceed its operational limits, potentially leading to memory corruption and system instability.
The technical implementation of this vulnerability involves a direct memory allocation failure where the kernel's PTP subsystem accepts user-defined parameters without sufficient validation to ensure they remain within the operational constraints of the underlying memory management system. When the system processes an excessively large value for max_vclocks, the kcalloc function attempts to allocate memory that surpasses the maximum allowed allocation size, causing the kernel to trigger a WARNING message and potentially resulting in a system crash or denial of service condition. This type of vulnerability falls under the category of buffer overflow conditions as defined by CWE-121, where insufficient boundary checking allows for improper memory handling that can be exploited to compromise system integrity.
The operational impact of CVE-2025-40057 extends beyond simple denial of service scenarios as it creates potential attack vectors that could be leveraged for privilege escalation or system compromise. An attacker who can manipulate the max_vclocks parameter through legitimate kernel interfaces or device drivers could potentially cause system instability or create conditions where malicious code could execute with elevated privileges. The vulnerability particularly affects systems running kernel versions that have not been patched, with the fix implementing additional guard mechanisms to prevent values from exceeding kcalloc's operational limits. This issue aligns with ATT&CK technique T1068 which covers privilege escalation through kernel vulnerabilities, and represents a critical weakness in the kernel's input validation and memory management protocols.
The recommended mitigations for this vulnerability include applying the official kernel patches that extend the guard mechanisms to properly validate the max_vclocks parameter against kcalloc's maximum allocation limits. System administrators should prioritize updating their kernel versions to include the patched code that prevents the problematic memory allocation scenarios. Additional protective measures involve implementing proper input validation at multiple layers of the system architecture, including kernel space and userspace interfaces that might interact with PTP subsystem parameters. The fix demonstrates proper defensive programming practices by establishing clear upper bounds and implementing comprehensive error checking that aligns with security best practices outlined in the Common Weakness Enumeration catalog. Organizations should also monitor for similar vulnerabilities in other kernel subsystems and ensure their patch management processes include timely application of security updates to prevent exploitation of similar memory handling flaws.