CVE-2026-92486 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Fix CFI mismatch in task work callback
BPF subprograms use the bpf_callback_t ABI, but task work invokes the callback through a three-argument function pointer. This trips kCFI.
Store and invoke the callback as bpf_callback_t.
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Analysis
by VulDB Data Team • 09/17/2026
The Linux kernel's eXpress Data Path (eBPF) subsystem provides a powerful mechanism for running sandboxed programs in the kernel, enabling high-performance networking, observability, and security functionalities without requiring module reloading or system reboots. A critical aspect of maintaining kernel integrity is Control Flow Integrity (CFI), specifically kCFI, which ensures that indirect function calls adhere to expected type signatures defined by compiler instrumentation. The vulnerability addressed involves a mismatch in the Application Binary Interface (ABI) used for invoking BPF callbacks within task work contexts. Specifically, while BPF subprograms are designed to utilize the bpf_callback_t ABI, the implementation of task work invoked these callbacks through a function pointer expecting three arguments rather than adhering strictly to the defined single-argument signature or standard calling convention associated with bpf_callback_t.
This discrepancy triggers kCFI violations because the runtime type checking enforced by Clang's CFI instrumentation detects that an indirect call is being made using a function pointer whose type does not match the target function's expected prototype. In environments where kCFI is enabled, such mismatches are treated as security-critical errors rather than mere warnings, potentially leading to kernel panics or denial of service conditions if the control flow integrity checks fail during execution. The root cause lies in how task work structures handle callback invocations; by passing extra arguments or using an incompatible pointer type, the code bypasses the strict typing guarantees that CFI relies upon to prevent control-flow hijacking attacks.
The operational impact of this vulnerability is primarily related to system stability and security posture when running eBPF programs under kCFI-enabled configurations. If triggered, it can cause immediate kernel crashes due to the enforcement mechanisms rejecting the invalid indirect call. Furthermore, even if not immediately exploitable for arbitrary code execution in all contexts, such ABI mismatches represent a deviation from secure coding practices that could potentially be leveraged by attackers to confuse control flow analysis tools or exploit undefined behavior in specific edge cases involving stack corruption or register state manipulation. The fix involves correcting the storage and invocation of the callback to strictly conform to the bpf_callback_t type definition, thereby ensuring compatibility with kCFI requirements and maintaining consistent calling conventions across all BPF execution paths.
From a vulnerability classification perspective, this issue aligns with CWE-841 Improper Enforcement of Behavioral Workflow or more specifically issues related to improper handling of function pointers which can fall under CWE-94 Improper Control of Generation of Code Command Injection if the mismatch leads to unintended code execution paths. In terms of MITRE ATT&CK mapping, while this is primarily a stability and integrity issue rather than an active exploit vector for lateral movement or privilege escalation in its current state, it relates to techniques involving binary manipulation or exploitation of compiler-enforced security features like Control Flow Guard equivalents found in modern operating systems. Mitigation strategies include applying the provided kernel patch that corrects the function pointer type usage within task work callbacks. Administrators should ensure their kernels are updated to versions containing this fix and verify that eBPF programs deployed in production environments do not rely on non-standard calling conventions for internal kernel interactions. Regular auditing of BPF program code against strict ABI standards helps prevent similar issues, ensuring that all indirect calls respect the type signatures enforced by modern compiler security features.