CVE-2026-64508 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Support for hardening against JIT spraying
The BPF JIT allocator packs many small programs into larger executable allocations and reuses space within those allocations as programs are loaded and freed. When fresh code is written into space that a previous program occupied, an indirect jump into the new program can reuse a branch prediction left behind by the old one.
Flush the indirect branch predictors before reusing JIT memory so that indirect jumps into a newly written program don't reuse predictions from an old program that occupied the same space.
Introduce bpf_arch_pred_flush_enabled static key and bpf_arch_pred_flush static call for flushing the branch predictors on JIT memory reuse. Architectures that need a flush, can update it to a predictor flush function. By default, its a NOP and does not emit any CALL.
Allocations larger than a pack are not covered by this flush. That is safe because cBPF programs (the unprivileged attack surface) are bounded well below a pack size. Issue a warning if this assumption is ever violated while the flush is active.
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Analysis
by VulDB Data Team • 07/26/2026
The vulnerability addressed in this Linux kernel patch relates to a critical security flaw in the Berkeley Packet Filter (BPF) Just-In-Time (JIT) compiler implementation that could enable attackers to exploit branch prediction mechanisms for privilege escalation. This issue specifically targets the BPF JIT allocator's memory management strategy where multiple small programs are packed into larger executable memory regions and reused as programs are loaded and freed. The core technical flaw lies in the improper handling of indirect branch predictors during memory reuse operations, creating a potential attack vector that leverages speculative execution behaviors to bypass security controls.
The vulnerability exploits a fundamental weakness in how the kernel manages executable memory regions for BPF JIT compilation, where memory space is efficiently packed and reused without proper clearing of branch prediction state. When new code is written into memory locations previously occupied by other programs, indirect jumps can inadvertently reuse stale branch predictions from the previous program that occupied the same memory space. This creates a scenario where an attacker could potentially manipulate branch predictor state to redirect execution flow through unintended code paths, effectively enabling a form of side-channel attack that bypasses traditional security boundaries.
The operational impact of this vulnerability is significant as it affects the integrity of the BPF JIT compiler's memory management system, potentially allowing malicious actors to exploit speculative execution behaviors for privilege escalation or information disclosure. The issue particularly affects systems running with BPF JIT enabled where unprivileged users could leverage this flaw to gain elevated privileges, making it a critical concern for kernel security. The vulnerability is especially dangerous because it operates at the kernel level and can be exploited through legitimate BPF program loading mechanisms without requiring special privileges beyond normal user access.
The fix implements a comprehensive solution that introduces a static key mechanism called bpf_arch_pred_flush_enabled and a corresponding static call bpf_arch_pred_flush to properly flush indirect branch predictors before reusing JIT memory. This approach allows architectures that require such flushing operations to register appropriate predictor flush functions while maintaining backward compatibility for systems where no flushing is necessary, as the default implementation is a NOP operation that does not emit any CALL instructions. The solution specifically targets the memory reuse scenario without affecting larger allocations that are already considered safe due to their size limitations.
Security implications extend beyond immediate privilege escalation potential as this vulnerability represents a classic example of a side-channel attack through speculative execution mechanisms, aligning with attack patterns documented in the ATT&CK framework under techniques related to privilege escalation through speculative execution. The implementation follows security best practices by introducing architecture-specific flushing capabilities while maintaining performance for systems that don't require such operations. The warning mechanism ensures that administrators are alerted if the assumption about cBPF program size limitations is violated, providing operational visibility into potential security risks. This vulnerability demonstrates the complexity of modern kernel security issues where seemingly benign memory management optimizations can create significant attack surfaces when combined with advanced CPU features like branch prediction and speculative execution. The mitigation addresses a specific CWE category related to improper handling of memory reuse in executable contexts and aligns with industry standards for protecting against side-channel attacks in kernel space operations.