CVE-2026-92515 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Preserve unique-field state across nested structs
btf_find_struct_field() initializes a fresh seen mask for every recursive descent. Unique special fields in different levels of the same aggregate therefore do not see one another. The duplicate fields can reach btf_parse_fields(), where they trigger an invariant WARN_ON_ONCE(). A crafted user BTF can consequently trigger the warning before map creation checks capabilities.
Initialize the seen mask once in btf_find_field() and pass the same pointer through struct, datasec, and nested-struct walks. This gives the entire field traversal one shared uniqueness state.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's Berkeley Packet Filter subsystem contains a logic flaw within its BTF type parsing mechanism that can lead to an unexpected kernel warning or potential denial of service conditions during map creation. The vulnerability centers on how the kernel handles unique-field identification across nested structures defined in BTF data. When processing complex aggregate types, such as structs containing other structs, the function btf_find_struct_field is responsible for identifying fields and ensuring that field names remain unique within their scope to prevent ambiguity. However, the original implementation initializes a fresh seen mask for every recursive descent into a nested struct level. This means that special or duplicate fields existing at different levels of nesting are treated as independent entities rather than being evaluated against a global uniqueness constraint for the entire aggregate structure.
This architectural oversight allows crafted user-space BTF data to introduce duplicate field names across nested layers without triggering immediate validation errors during the initial parsing phase. These duplicates subsequently reach the btf_parse_fields function, where they violate an internal invariant check implemented via WARN_ON_ONCE(). While this specific warning may not always result in a full kernel panic depending on configuration and context, it represents a significant stability issue that can disrupt system operations or be leveraged for denial of service attacks by flooding logs with warnings or causing unexpected state changes. Crucially, because this validation occurs before map creation checks capabilities, an unprivileged user might trigger these conditions without having the necessary privileges to create maps, highlighting a gap in privilege escalation controls and input sanitization timing.
The root cause is classified under CWE-20 as Improper Input Validation, specifically regarding the failure to maintain consistent state across recursive data structures during parsing. From a threat modeling perspective aligned with MITRE ATT&CK techniques, this vulnerability relates to T1564.008 Hidden Processes and Files or more broadly to exploitation of logic flaws in system components that can lead to availability impacts. The issue stems from the lack of shared context between recursive calls, which is a common pitfall when handling deeply nested data structures without proper state management across recursion levels.
To mitigate this vulnerability, the kernel developers have implemented a fix that initializes the seen mask once at the entry point btf_find_field and passes the same pointer through all subsequent struct, datasec, and nested-struct walks. This ensures that the entire field traversal operates with one shared uniqueness state, effectively preventing duplicate fields from being accepted across different nesting levels of the same aggregate type. System administrators should ensure their Linux kernels are updated to versions containing this patch. Additionally, organizations relying on eBPF programs for security monitoring or network filtering should validate all BTF inputs rigorously in user-space before passing them to the kernel as a defense-in-depth measure, ensuring that no malformed or maliciously crafted structures can reach the vulnerable parsing logic even if future edge cases are discovered.