Linux Kernel mseal Invariant Violation (Linux kernel 6.17-7.0 rc5)

Title : CVE-2026-23416 - Linux Kernel mseal Invariant Violation (Linux kernel 6.17-7.0 rc5) Exploit Poc : https://github.com/bluedragonsecurity/CVE-2026-23416-POC Discovered by : Antonius (w1sdom) Web : www.bluedragonsec.com Github : https://github.com/bluedragonsecurity Date of Discovery : March 27 2026 Overview An invariant violation (VM_WARN_ON_VMG) fires at mm/vma.c:830 inside vma_merge_existing_range() when mseal(2) is called with a range spanning two adjacent VMAs where one has VM_SEALED set and the other does not. Affected Versions Linux kernel 6.17 through Linux kernel 7.0-rc5 (confirmed). Call Path The vulnerability is triggered through the following call chain: mseal(2) → do_mseal() in mm/mseal.c → mseal_apply() → vma_modify_flags() in mm/vma.c → vma_modify() → vma_merge_existing_range(), where the VM_WARN_ON_VMG assertion fires at line 830. Root Cause do_mseal() calls vma_modify_flags() with the original mseal() start address without clamping it to the current VMA's vm_start when the mseal range spans two VMAs with different VM_SEALED states. This causes vma_merge_existing_range() to receive an inconsistent vmg state, triggering the assertion: vmg->start != middle->vm_start. github Security Relevance The bug is reachable from unprivileged userspace (UID 1000, no capabilities required — only memfd_create, mmap, and mseal syscalls are needed). Since mseal(2) is itself a security primitive protecting VMA immutability, an invariant violation in its application logic means VM_SEALED may be applied incorrectly when spanning VMAs with mixed seal states, potentially undermining the security guarantee mseal provides. In production kernels where WARN compiles to a no-op, the inconsistent vmg state proceeds silently — the VMA tree could be left with incorrect seal state without any visible error. Exploitation Characteristics - Access required: Unprivileged (UID 1000, no CAP_*) - Reproducibility: 100% deterministic, triggers in under 1 second, no fault injection needed - Impact: Silent corruption of VMA seal state in production kernels, potentially allowing sealed memory regions to be incorrectly modified