CVE-2026-93148 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject MEM_ALLOC BTF accesses past object bounds
BTF struct walks relax the struct-size check for accesses through a trailing flexible array. That is valid for ordinary BTF type walking, but PTR_TO_BTF_ID | MEM_ALLOC values point to objects allocated with the static BTF type size.
When walking a MEM_ALLOC object, reject the access before applying the flexible-array relaxation if the access range extends past the struct size. Apply the same policy to struct ID matching so kfunc and kptr type checks do not walk past the allocated object bounds either.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel's eBPF subsystem enforces strict memory safety guarantees through its verifier, which analyzes bytecode before execution to prevent invalid memory accesses. A specific vulnerability was identified in how the verifier handles BTF (BPF Type Format) struct walks involving flexible arrays when applied to objects allocated with static sizes. The core technical flaw lies in an overly permissive check for trailing flexible array members during type walking operations. Normally, the kernel relaxes structural size checks to allow access through a trailing flexible array because such structures are often dynamically sized at runtime. However, this relaxation was incorrectly applied to pointers tagged as PTR_TO_BTF_ID with MEM_ALLOC flags, which represent objects allocated based on the static BTF type definition rather than dynamic sizing logic.
This discrepancy creates a scenario where the verifier fails to reject memory accesses that extend beyond the actual bounds of the statically allocated object. When an eBPF program attempts to read or write through such a pointer using a flexible array member offset, the kernel does not properly validate whether the access range exceeds the fixed size defined in the BTF metadata. This oversight allows for out-of-bounds memory reads and writes within the context of the running eBPF program. The flaw affects both general struct ID matching logic as well as specific checks related to kfuncs and kptr types, meaning that any code path relying on these mechanisms could potentially bypass boundary validation if it involves flexible array members in statically allocated structures.
The operational impact of this vulnerability is significant due to the privileged nature of eBPF execution environments. Although eBPF programs run in a sandboxed kernel context, successful exploitation can lead to arbitrary memory corruption or information disclosure within the kernel space. An attacker with the ability to load malicious eBPF programs could leverage this flaw to read sensitive kernel data structures that reside immediately after the allocated object or corrupt adjacent memory regions. This undermines the integrity of the kernel and potentially allows for privilege escalation if combined with other vulnerabilities, as it breaks the fundamental isolation guarantees provided by the BPF verifier.
To mitigate this risk, the Linux kernel maintainers have implemented a fix that explicitly rejects MEM_ALLOC accesses before applying the flexible-array relaxation logic. The updated code now checks if the access range extends past the struct size defined in the static BTF type and denies such operations outright. This ensures that kfunc and kptr type checks also adhere to strict boundary validation, preventing walks past allocated object bounds. System administrators should apply kernel updates containing this patch immediately to restore proper memory safety guarantees for eBPF programs.
From a classification perspective, this vulnerability aligns with CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write, as the core issue involves accessing memory outside of allocated boundaries due to insufficient validation logic. In terms of attack vectors, it relates to MITRE ATT&CK technique T1068 Exploitation for Privilege Escalation, since kernel-level memory corruption is a common precursor to gaining higher privileges on compromised systems. The fix reinforces the principle of least privilege by ensuring that eBPF programs cannot exploit ambiguities in type definitions to bypass security controls designed to protect kernel memory integrity.