CVE-2026-98454 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix create context out-of-bounds reads
smb2_parse_contexts() validates the complete create-context area but does not limit each record to its Next field before dispatching it. A malformed chain can therefore expose bytes beyond the current context to a handler. The QFid handler also used a full response-structure cast although it only reads DiskFileId.
The SMB2/SMB3 lease parsers made the same layout assumption: they read LeaseState and LeaseFlags at canonical offsets rather than at DataOffset. A valid non-canonical DataOffset could therefore yield unrelated in-bounds data, while a short DataLength was still accepted.
Limit each context to its Next value, reject offsets before the context header, and reject malformed chains. Bound the name range by the current context and do not dispatch a known handler when DataLength is zero. Read the QFid DiskFileId only when the context data covers that field. Parse the lease context from DataOffset and require DataLength to match the v1 or v2 lease_context size used by ksmbd. A size mismatch skips lease parsing without failing the open.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel SMB client implementation contained a critical class of out-of-bounds read vulnerabilities within its context parsing logic, specifically affecting how create contexts and lease information are processed during file operations. These flaws stemmed from insufficient validation of data boundaries when iterating through chains of SMB2 or SMB3 protocol structures. The core issue lies in the function smb2_parse_contexts(), which validates the overall size of the create-context area but fails to enforce strict limits on individual records based on their Next field pointers. This oversight allows a maliciously crafted server response containing malformed context chains to expose memory bytes beyond the intended scope of the current context record to internal handlers, leading to potential information disclosure or kernel instability depending on how those exposed bytes are interpreted by subsequent processing logic.
A specific instance of this flaw involves the QFid handler, which incorrectly utilized a full response-structure cast despite only requiring access to the DiskFileId field. This mismatch between the assumed structure size and actual data requirements increases the risk of reading unintended memory regions if the context boundaries are not strictly enforced. Similarly, the SMB2 and SMB3 lease parsers exhibited analogous vulnerabilities by assuming canonical offsets for fields such as LeaseState and LeaseFlags rather than respecting dynamic DataOffset values specified in the protocol headers. When a server provides a valid but non-canonical DataOffset, or when DataLength is shorter than expected, these parsers could yield unrelated in-bounds data from adjacent memory structures. This behavior violates fundamental principles of safe buffer handling and creates opportunities for attackers to probe kernel memory states through carefully crafted network packets that exploit the lack of rigorous boundary checks during context dispatching.
From a security standards perspective, this vulnerability aligns with CWE-125, which describes out-of-bounds read conditions where software reads data past the end or before the beginning of the intended buffer. In the context of attack techniques, these flaws relate to ATT&CK technique T1083, File and Directory Discovery, as successful exploitation could potentially allow an attacker to gather sensitive information about the system's memory layout or internal state through side-channel effects resulting from improper data exposure. The vulnerability primarily impacts systems running Linux kernels with SMB client capabilities enabled, particularly those interacting with untrusted or compromised SMB servers that can inject maliciously formatted context chains into file open requests.
The operational impact of these vulnerabilities includes potential kernel panics due to invalid memory access patterns triggered by the out-of-bounds reads, as well as information disclosure where sensitive data from adjacent kernel structures might be leaked back through protocol responses if not properly masked or handled. Mitigation strategies involve applying vendor-provided kernel updates that patch smb2_parse_contexts() and related lease parsing functions. The fix ensures each context is strictly limited to its Next value boundaries, rejects offsets pointing before the context header, and validates malformed chains more rigorously. Additionally, the name range within contexts is now bounded by the current context scope, preventing handlers from accessing data outside their designated area. Known handlers are no longer dispatched when DataLength is zero, eliminating unnecessary processing of empty or invalid payloads. For QFid operations, DiskFileId reading is conditional upon sufficient context data coverage, ensuring that only valid portions of the structure are accessed. Lease parsing has been corrected to read from the specified DataOffset and requires DataLength to match expected lease_context sizes for v1 or v2 protocols; mismatches now result in skipping lease parsing without failing the entire open operation, thereby maintaining service availability while preventing exploitation attempts through malformed length fields.