CVE-2026-43333 in Linux
Summary
by MITRE • 05/08/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: reject direct access to nullable PTR_TO_BUF pointers
check_mem_access() matches PTR_TO_BUF via base_type() which strips PTR_MAYBE_NULL, allowing direct dereference without a null check.
Map iterator ctx->key and ctx->value are PTR_TO_BUF | PTR_MAYBE_NULL. On stop callbacks these are NULL, causing a kernel NULL dereference.
Add a type_may_be_null() guard to the PTR_TO_BUF branch, matching the existing PTR_TO_BTF_ID pattern.
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Analysis
by VulDB Data Team • 09/13/2026
The vulnerability resides within the Linux kernel's eBPF subsystem where a critical flaw exists in the memory access validation mechanism. This issue specifically affects how the kernel handles nullable pointer types during BPF program execution, creating a potential pathway for kernel crashes and privilege escalation. The problem manifests when the check_mem_access() function processes PTR_TO_BUF type pointers, as it employs base_type() to strip away the PTR_MAYBE_NULL attribute, effectively removing the null check mechanism that should prevent direct dereference operations on potentially null pointers.
The technical flaw stems from a mismatch in type handling logic within the BPF verifier component. When map iterator contexts are processed, the ctx->key and ctx->value fields are initialized with PTR_TO_BUF | PTR_MAYBE_NULL type attributes, indicating they may contain null values. However, during stop callback execution, these same fields become NULL, creating a scenario where the kernel attempts to dereference a null pointer without proper validation. This direct access to nullable buffer pointers bypasses the normal null check mechanisms that would typically prevent such operations, leading to kernel NULL dereference conditions that can result in system crashes or, in more severe cases, privilege escalation.
The operational impact of this vulnerability extends beyond simple system instability, as it represents a potential attack vector for malicious actors seeking to exploit kernel memory management flaws. When an eBPF program executes with malicious intent, it could leverage this vulnerability to trigger kernel crashes or potentially escalate privileges by manipulating the memory access patterns. The flaw particularly affects systems running kernel versions where eBPF programs can be loaded and executed, making it relevant to a wide range of Linux distributions and server environments. This vulnerability aligns with CWE-476 which addresses null pointer dereference issues in software systems, and could potentially map to ATT&CK technique T1059.006 for kernel-mode exploitation.
The mitigation strategy involves implementing a type_may_be_null() guard specifically within the PTR_TO_BUF branch of the memory access validation logic. This approach mirrors the existing pattern already used for PTR_TO_BTF_ID type handling, ensuring consistency in how nullable pointer types are managed throughout the kernel's BPF subsystem. By adding this additional null check guard, the kernel prevents direct dereference operations on PTR_TO_BUF pointers that may legitimately contain null values, thereby eliminating the kernel NULL dereference condition that was previously possible. The fix essentially restores proper null validation semantics that should have been maintained when processing nullable buffer pointers, aligning the implementation with the expected behavior of the type system and preventing the escalation of memory access violations into system-wide crashes or security breaches.