CVE-2026-98628 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
bpf: Make post-verification instruction rewrites killable
After do_check() returns, the verifier runs several instruction rewrite passes. Some of them patch or remove one instruction at a time. Each operation moves the remaining instruction and auxiliary-data arrays and adjusts all branch offsets, making the overall work quadratic in the program length.
A privileged loader can submit 131072 unconditional jumps by zero followed by a valid return. Verification finishes quickly, but bpf_opt_remove_nops() then spends a long time removing each jump separately. Since this post-verification work neither checks for signals nor reschedules, a pending SIGKILL cannot terminate the task until the rewrite finishes.
Make bpf_patch_insn_data() and verifier_remove_insns() common cancellation and rescheduling points. These helpers run from BPF_PROG_LOAD process context, and bpf_patch_insn_data() can already sleep while reallocating auxiliary data.
Report interrupted constant blinding as -EINTR and propagate it through both JIT paths, including kernels that permit interpreter fallback. Other blinding failures retain the existing fallback behavior.
This does not reduce the quadratic cost of the rewrite passes, but it makes the work preemptible and allows a killed loader to be torn down promptly.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel BPF subsystem contains a vulnerability related to unbounded computational complexity during post-verification instruction rewriting, which can lead to denial-of-service conditions for privileged processes. The issue arises after the initial verification phase completes successfully via do_check(), where the verifier executes several passes to rewrite or remove instructions. Specifically, operations such as patching or removing individual instructions require shifting remaining instruction and auxiliary data arrays while adjusting branch offsets. This process results in quadratic time complexity relative to the program length. A malicious privileged user can exploit this by submitting a BPF program consisting of 131072 unconditional jumps followed by a valid return statement. While the initial verification completes quickly, the subsequent bpf_opt_remove_nops() function spends an excessive amount of time removing each jump individually because it lacks mechanisms to check for pending signals or reschedule execution. Consequently, if a SIGKILL signal is sent to the loader process, the task cannot be terminated promptly until the quadratic rewrite operation finishes entirely, effectively allowing a privileged user to hang system resources indefinitely through resource exhaustion.
This vulnerability aligns with CWE-400, which describes uncontrolled resource consumption leading to denial of service, and can be mapped to MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under the sub-category of Resource Exhaustion: Oscillating Attack or similar persistent load generation. The core flaw is not in the verification logic itself but in the lack of interruptibility during post-verification optimization passes that operate within process context without yielding to the scheduler or checking for termination signals. This allows a local attacker with sufficient privileges to create a sustained denial-of-service condition by forcing the kernel into an unbounded loop that ignores standard signal handling mechanisms, thereby preventing timely cleanup and potentially impacting system stability or other running processes due to CPU starvation.
The resolution involves modifying bpf_patch_insn_data() and verifier_remove_insns() to serve as common cancellation and rescheduling points within the BPF_PROG_LOAD process context. Since these helpers already have the capability to sleep during auxiliary data reallocation, they are suitable locations for implementing preemptibility checks. The fix ensures that if an interrupt occurs, such as a SIGKILL signal, the operation is aborted promptly rather than continuing until completion. Additionally, interrupted constant blinding operations now return -EINTR and propagate this error code through both JIT compilation paths, including scenarios where interpreter fallback is permitted. This change does not reduce the inherent quadratic cost of the rewrite passes but fundamentally changes their execution model to be preemptible, allowing killed loader processes to be torn down immediately without waiting for lengthy computational tasks to finish.
To mitigate similar risks in BPF programs and kernel extensions, developers should ensure that long-running verification or optimization loops include periodic checks for pending signals and scheduler rescheduling points. System administrators can monitor for unusual CPU usage patterns associated with BPF program loading operations, particularly from privileged accounts, as an indicator of potential abuse. While the immediate fix addresses the specific quadratic rewrite issue by adding interruptibility, ongoing vigilance is required to prevent other forms of resource exhaustion in kernel subsystems that process untrusted or user-supplied code structures. Regular updates to the Linux kernel are essential to maintain these protections against local privilege escalation and denial-of-service attacks targeting BPF infrastructure.