CVE-2026-92477 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
scsi: ufs: debugfs: Reserve space for a string terminator
ufs_saved_err_write() copies user input into a zero-initialized stack buffer and passes it to kstrtoint(). A write that fills the entire buffer overwrites its only terminator.
Reject an input whose length leaves no room for the trailing NUL.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Linux kernel's SCSI UFS subsystem involves a critical memory safety flaw within the debugfs interface, specifically affecting the ufs_saved_err_write function. This component is responsible for handling user-space inputs that are written to specific debug files intended for diagnostic purposes during development or troubleshooting phases. The core technical issue stems from an improper buffer management strategy where user-supplied data is copied into a stack-allocated buffer that has been zero-initialized. While the initialization suggests an intent to ensure null termination, the implementation fails to account for the length of the incoming input relative to the fixed size of the destination buffer. When a write operation provides data that exactly fills the entire capacity of this buffer, it overwrites the final byte which serves as the mandatory string terminator or NUL character. This results in a scenario where the resulting string lacks proper termination, leading to potential out-of-bounds reads when subsequent functions attempt to process the string based on standard C-string conventions.
From a technical perspective, this flaw represents a classic buffer overflow condition that manifests specifically through off-by-one errors and improper bounds checking during input validation. The function kstrtoint is subsequently invoked to parse the integer value from the provided string. If the string lacks its terminating NUL character due to the overwrite described above, functions relying on strlen or similar traversal mechanisms may read beyond the allocated stack frame boundaries. This can lead to information disclosure by leaking adjacent kernel memory contents into user space if those bytes are interpreted and returned as part of a response, or it could potentially cause a denial of service through a kernel panic resulting from accessing invalid memory addresses. Although debugfs interfaces are typically restricted to root users with high privileges, the principle of least privilege and defense in depth dictates that even privileged interfaces must not compromise system stability or integrity. The vulnerability aligns closely with CWE-120 Buffer Copy without Checking Size of Input Classic Buffer Overflow and CWE-134 Use of Externally-Controlled Format String if the malformed data influences parsing logic, though primarily it is a memory safety violation categorized under improper input validation leading to buffer overruns.
The operational impact of this vulnerability is contingent upon the attacker's ability to interact with the debugfs interface. Since access to these files generally requires root-level privileges or specific capabilities within the Linux security model, the direct exploitation risk for remote attackers is negligible unless there are other privilege escalation vectors present that allow an unprivileged user to gain write access to kernel debug interfaces. However, in environments where developers or system administrators routinely interact with such diagnostic tools, a local attacker who has obtained root access could potentially trigger this flaw to destabilize the kernel. The primary consequence remains a denial of service via kernel crash or panic due to invalid memory access during string processing operations that expect null-terminated inputs. There is also a theoretical risk of information leakage if the out-of-bounds read retrieves sensitive kernel data structures adjacent to the stack buffer, although this would depend heavily on the specific compiler optimizations and runtime state at the moment of exploitation.
To mitigate this vulnerability, the Linux kernel maintainers have implemented a strict input length validation check within the ufs_saved_err_write function. The fix ensures that any write operation requesting more space than is available for both data and the trailing NUL terminator is rejected immediately. This approach enforces proper bounds checking before any memory copy operations occur, thereby preventing the overwrite of critical stack metadata or adjacent variables. Administrators should ensure their systems are updated with kernel patches that include this fix to maintain system integrity. Furthermore, security best practices recommend restricting access to debugfs interfaces in production environments by mounting them with appropriate permissions or disabling unnecessary debugging features entirely when not actively troubleshooting issues. This reduces the attack surface and ensures that even if similar vulnerabilities exist in other subsystems, they cannot be easily triggered by unauthorized users. Adhering to these standards aligns with general secure coding principles emphasized in industry frameworks such as OWASP guidelines for input validation and MITRE ATT&CK techniques related to privilege escalation via local exploits, ensuring robust defense against memory corruption attacks.