CVE-2026-89792 in Linux
Summary
by MITRE • 09/16/2026
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: prevent out-of-bounds reads in share config responses
Validate IPC share configuration payload sizes before consuming variable-length fields. Bound veto list parsing and account for the separator byte when deriving the path length.
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Analysis
by VulDB Data Team • 09/16/2026
The ksmbd component within the Linux kernel, which provides an implementation of the Server Message Block protocol to facilitate file sharing between Unix-like systems and Windows clients, contained a critical input validation flaw in its handling of IPC share configuration responses. This vulnerability stems from insufficient boundary checks when processing variable-length fields embedded within network packets received during SMB negotiation or session setup phases. Specifically, the code failed to rigorously validate the size of the IPC share configuration payload before attempting to parse and consume these dynamic data structures. By not enforcing strict length constraints on incoming payloads, the kernel allowed attackers to craft maliciously sized packets that could trigger out-of-bounds reads when the system attempted to interpret field lengths or iterate through list elements based on untrusted input values.
The technical root cause of this issue lies in the parsing logic for veto lists and path derivation within the share configuration response handler. When processing these structures, the implementation did not adequately account for separator bytes that delimit components within the payload. This oversight meant that calculations determining the length of subsequent fields or paths could exceed the actual allocated buffer size or the bounds of the received packet data. Consequently, an attacker who can interact with the ksmbd service over a network connection could exploit this logic error to read memory contents beyond the intended boundaries of the configuration structures. Such out-of-bounds reads do not typically allow for direct code execution but serve as a powerful information disclosure vector, potentially exposing sensitive kernel memory states or internal data structures that were not meant to be accessible via standard SMB operations.
From an operational perspective, this vulnerability poses a significant risk to system integrity and confidentiality. While the immediate impact is primarily informational leakage rather than remote code execution, the exposure of kernel memory can aid attackers in developing more sophisticated exploits by revealing stack canaries, function pointers, or other security mitigations deployed within the operating system. Furthermore, repeated exploitation attempts could contribute to resource exhaustion or instability if the malformed data triggers unexpected error handling paths that degrade service availability. The flaw is particularly concerning because ksmbd operates as a network-facing service, meaning it is accessible to remote adversaries without requiring prior authentication in many default configurations, thereby expanding the attack surface significantly compared to local-only vulnerabilities.
This vulnerability aligns with CWE-125, which describes Out-of-Bounds Read, where software reads data past the end or before the beginning of the intended buffer. In terms of offensive security frameworks, this flaw facilitates reconnaissance and information gathering activities categorized under ATT&CK technique T1083, File and Directory Discovery, as it allows an attacker to extract internal system details that can inform further exploitation steps. To mitigate this risk, administrators should ensure that their Linux distributions are updated with the latest kernel patches that include fixes for ksmbd input validation logic. Additionally, deploying network-level access controls such as firewalls or intrusion detection systems to restrict SMB traffic to trusted subnets and clients reduces the exposure surface. Regular auditing of smb.conf configurations to disable unnecessary IPC shares can also minimize potential attack vectors associated with this component until all systems are fully patched.