CVE-2025-21964 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
cifs: Fix integer overflow while processing acregmax mount option
User-provided mount parameter acregmax of type u32 is intended to have an upper limit, but before it is validated, the value is converted from seconds to jiffies which can lead to an integer overflow.
Found by Linux Verification Center (linuxtesting.org) with SVACE.
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability CVE-2025-21964 represents a critical integer overflow flaw within the Linux kernel's CIFS (Common Internet File System) implementation that directly impacts the security and stability of network file sharing operations. This issue specifically affects the processing of the acregmax mount option, which controls the maximum time a client will wait for a response to a registration request during CIFS operations. The flaw exists in the kernel's handling of user-provided mount parameters, where the u32 type value intended to be bounded by an upper limit undergoes an unsafe conversion to jiffies before validation occurs. This conversion process creates a scenario where malicious or malformed input can cause the integer overflow, potentially leading to unpredictable behavior in the kernel's memory management and network operations.
The technical execution of this vulnerability stems from the improper validation sequence within the CIFS mount parameter processing logic. When users specify the acregmax parameter during CIFS mount operations, the kernel converts this value from seconds to jiffies for internal processing. The integer overflow occurs because the conversion process does not properly check for overflow conditions before performing the arithmetic operation that transforms the user-provided seconds value into jiffies. This flaw allows attackers to potentially manipulate the mount option in ways that could cause the kernel to process invalid values, leading to potential memory corruption or other undefined behaviors. The vulnerability is particularly concerning because it operates at the kernel level where such flaws can result in privilege escalation or system instability. The issue was identified through systematic analysis by the Linux Verification Center using SVACE tools, highlighting the importance of formal verification in kernel security.
The operational impact of CVE-2025-21964 extends beyond simple denial of service scenarios to potentially enable more sophisticated attack vectors. An attacker who can influence the CIFS mount process could exploit this integer overflow to cause kernel memory corruption, leading to system crashes or potentially allowing for privilege escalation depending on the specific memory layout and execution context. The vulnerability affects systems running Linux kernels that support CIFS network file sharing, particularly those that allow user-controlled mount options. Since CIFS is commonly used in enterprise environments for file sharing and collaboration, this flaw could be leveraged to disrupt critical network services or create persistent access points within networked systems. The flaw's potential for exploitation increases when combined with other kernel vulnerabilities or when attackers can manipulate mount parameters through automated tools or compromised services that utilize CIFS functionality.
Mitigation strategies for CVE-2025-21964 should focus on immediate kernel updates and parameter validation hardening. System administrators should prioritize applying the relevant kernel patches that address the integer overflow in the CIFS acregmax parameter handling, as these updates typically include proper bounds checking before conversion to jiffies. Additionally, organizations should implement strict controls over CIFS mount options and user permissions, particularly in environments where untrusted users might be able to influence mount parameters. The implementation of proper input validation and bounds checking for all mount options should be enforced across network file systems to prevent similar issues. Security monitoring should include detection of unusual or potentially malicious mount parameter values, particularly when these parameters are derived from user input. The vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and could potentially map to ATT&CK technique T1059.007 for command and scripting interpreter usage in exploitation scenarios. Organizations should also consider implementing network segmentation and access controls to limit exposure of CIFS services to untrusted networks or users, reducing the attack surface for such kernel-level vulnerabilities.