CVE-2026-93144 in Linux
Summary
by MITRE • 09/18/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Reject writes through untrusted BTF pointers
check_ptr_to_btf_access() lets program-type btf_struct_access callbacks validate writes before the default BTF access path rejects non-read accesses. That bypasses the read-only policy for untrusted BTF pointers created by helpers such as bpf_rdonly_cast().
Reject non-read accesses through PTR_UNTRUSTED BTF pointers at the common entry point, before the callback branch to handle all cases.
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Analysis
by VulDB Data Team • 09/18/2026
The Linux kernel's eBPF subsystem implements a sophisticated type safety mechanism known as BPF Type Format or BTF to ensure that programs interact with kernel data structures in a safe and predictable manner. A critical security flaw was identified within this framework, specifically concerning the validation logic for pointer types marked as untrusted. The vulnerability stems from an inconsistency in how write operations are handled when they involve pointers derived through specific casting helpers such as bpf_rdonly_cast(). These helpers are designed to create read-only views of kernel data structures, effectively enforcing a policy that prevents programs from modifying sensitive or immutable system state. However, the existing validation path allowed certain program types to bypass this restriction by invoking custom BTF structure access callbacks before the default security checks could reject non-read accesses.
The technical root cause lies in the execution order and scope of the check_ptr_to_btf_access function within the kernel source code. This function serves as a gatekeeper for accessing fields within BTF-annotated structures. For specific program types, it delegates validation to specialized callbacks that implement btf_struct_access logic. These callbacks were permitted to validate write operations before the broader system enforced the read-only policy associated with untrusted pointers. Consequently, an eBPF program could exploit this gap by using a pointer cast as read-only via bpf_rdonly_cast(), yet still perform write operations through these specialized callback paths. This effectively nullified the intended security boundary, allowing programs to modify data that should have been protected from modification due to their untrusted status or explicit read-only designation.
The operational impact of this vulnerability is significant for system stability and integrity. By permitting unauthorized writes to kernel memory regions via eBPF programs, an attacker could potentially corrupt critical kernel structures, alter security policies, or escalate privileges if the modified data influences control flow decisions within the kernel. This represents a classic violation of the principle of least privilege, where a component granted limited read access is able to perform write operations due to implementation flaws in the enforcement mechanism. The flaw affects systems running vulnerable versions of the Linux kernel that utilize eBPF with BTF annotations and employ helpers like bpf_rdonly_cast() for data inspection tasks.
To mitigate this risk, the vulnerability has been addressed by modifying the common entry point for BTF pointer access checks to reject non-read accesses through PTR_UNTRUSTED pointers before any specialized callback logic is invoked. This ensures that all write attempts are blocked at a centralized location regardless of the program type or specific validation path taken. Administrators should apply kernel updates provided by their distribution vendors as soon as possible. From a defensive perspective, organizations relying on eBPF for observability and security monitoring must ensure they are using patched kernels to prevent potential exploitation through crafted BTF programs that attempt to bypass read-only constraints.
This issue is categorized under CWE-20 Improper Input Validation because the system failed to properly validate access permissions based on pointer attributes before allowing operations. It also aligns with ATT&CK technique T1059 Command and Scripting Interpreter, specifically regarding eBPF program execution, where an attacker might use malicious scripts or programs to interact with kernel internals in unauthorized ways. The fix reinforces the integrity of the BTF type system by ensuring that access control policies are applied consistently across all code paths involved in pointer dereferencing and field access within the Linux kernel environment.