CVE-2026-90177 in Linux
Summary
by MITRE • 09/17/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Check pointer type for all atomic RMW paths
Atomic RMW verification records an instruction pointer type only when the current destination is PTR_TO_ARENA. A second path can therefore reach the same instruction with an ordinary pointer without comparing it against the saved arena type.
The post-verification fixup uses the saved type to rewrite the instruction to BPF_PROBE_ATOMIC for every path. Record the actual destination type for all atomic RMW paths so the existing mismatch check rejects incompatible uses of one instruction.
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Analysis
by VulDB Data Team • 09/18/2026
This vulnerability resides within the Linux kernel's Berkeley Packet Filter (BPF) subsystem, specifically affecting the verification logic for atomic read-modify-write operations. The BPF verifier is a critical security component responsible for ensuring that eBPF programs are safe to execute in kernel space by preventing invalid memory accesses and other unsafe behaviors. In this specific instance, the flaw lies in how the verifier tracks pointer types during the validation of atomic instructions. When processing an atomic read-modify-write operation, the verification process records the instruction's destination type only if that destination is identified as a PTR_TO_ARENA pointer type. This conditional recording creates a gap in the security model because it fails to capture the actual pointer context for other valid but non-arena pointer types.
The operational impact of this oversight allows an attacker or a maliciously crafted eBPF program to exploit the inconsistency in type tracking. A second execution path can reach the same atomic instruction with an ordinary, non-arena pointer without triggering the necessary comparison against the saved arena type that was recorded during the first path's verification. Because the verifier does not consistently record and compare the actual destination type across all paths leading to a single atomic operation, it may incorrectly assume compatibility where none exists. This leads to a situation where incompatible uses of an instruction are accepted by the verifier, potentially allowing unauthorized memory access or data corruption within kernel space.
From a technical perspective, this issue represents a classic case of incomplete verification logic in type-sensitive systems. The failure to record the actual destination type for all atomic read-modify-write paths means that the post-verification fixup mechanism cannot reliably rewrite instructions to BPF_PROBE_ATOMIC with confidence regarding their safety across different execution contexts. By recording the actual destination type universally, the existing mismatch check can properly reject incompatible uses of one instruction, thereby closing this loophole in the verification process. This ensures that every path leading to an atomic operation is subjected to rigorous type checking against a consistent baseline.
This vulnerability aligns with CWE-20, which describes Improper Input Validation, as the verifier failed to adequately validate and track pointer types across all possible execution paths. Furthermore, it relates to CWE-841, Improvement of Insufficient Enforcement of Behavioral Restrictions, because the enforcement mechanism for atomic operation safety was incomplete due to conditional logic that skipped necessary checks in certain scenarios. In terms of MITRE ATT&CK mapping, this type of kernel-level verification bypass can facilitate privilege escalation or denial-of-service attacks by allowing malicious code to execute with higher privileges than intended or cause system instability through invalid memory operations.
To mitigate this vulnerability, the Linux kernel has been updated to ensure that pointer types are checked for all atomic read-modify-write paths regardless of whether they involve PTR_TO_ARENA pointers. This fix ensures that the verifier consistently records and compares destination types, thereby preventing incompatible instruction usage from being accepted during verification. System administrators should apply the latest available kernel patches or updates provided by their distribution vendors to resolve this issue. Regularly updating the operating system is essential to maintain the integrity of the BPF subsystem and prevent potential exploitation of such logic flaws in high-performance networking and security monitoring applications that rely on eBPF programs.