CVE-2026-64579 in Linux
Summary
by MITRE • 08/05/2026
In the Linux kernel, the following vulnerability has been resolved:
xfrm: policy: preallocate inexact bins before xfrm_hash_rebuild reinsert
xfrm_hash_rebuild()'s first loop preallocates the bins/chains the reinsert loop needs, so the reinsert (after hlist_del_rcu()) cannot allocate or fail. But its guard is inverted: it skips policies with prefixlen < threshold and preallocates for the rest.
prefixlen < threshold is exactly when policy_hash_bysel() returns NULL and the reinsert takes the allocating xfrm_policy_inexact_insert() path. So the loop preallocates for the exact policies (which never allocate) and skips the inexact ones, whose bin/node is then allocated GFP_ATOMIC during reinsert. On failure the error path only WARN_ONCE()s and continues, leaving a poisoned bydst node; the next rebuild's hlist_del_rcu() dereferences LIST_POISON2 and takes a GPF. Reachable under memory pressure, deterministic via failslab.
Invert the guard so preallocation covers exactly the reinserted policies; the reinsert then allocates nothing and cannot fail.
Crash: Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI
KASAN: maybe wild-memory-access in range [0xdead...]
... Workqueue: events xfrm_hash_rebuild RIP: 0010:xfrm_hash_rebuild+0x5b3/0x1190 RAX: dead000000000122 (LIST_POISON2 + offset) ... Call Trace: hlist_del_rcu (include/linux/rculist.h:599) xfrm_hash_rebuild (net/xfrm/xfrm_policy.c:1365) process_one_work (kernel/workqueue.c:3322) worker_thread (kernel/workqueue.c:3486) kthread (kernel/kthread.c:436) ret_from_fork (arch/x86/kernel/process.c:158) ret_from_fork_asm (arch/x86/entry/entry_64.S:245) ... Kernel panic - not syncing: Fatal exception in interrupt
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Analysis
by VulDB Data Team • 08/05/2026
The vulnerability resides within the Linux kernel's IPsec framework, specifically in the xfrm policy hash management system. This flaw manifests in the xfrm_hash_rebuild function where improper preallocation logic creates a race condition leading to memory allocation failures during policy reinsertion. The issue stems from an inverted conditional check that determines which policies should receive preallocated hash bins before the rebuild process begins.
The technical implementation flaw involves the xfrm_hash_rebuild function's first loop which attempts to preallocate memory for hash bins needed during the subsequent reinsert operation. However, due to the inverted guard condition, the function preallocates memory for exact match policies while skipping those with prefix lengths below a certain threshold. This creates a critical mismatch because policies with prefixlen < threshold are precisely those that would trigger the non-allocating xfrm_policy_inexact_insert() path during reinsertion.
According to CWE-457, this represents a use of uninitialized memory vulnerability where the system attempts to access memory locations that were never properly initialized or allocated. The flaw also aligns with ATT&CK technique T1068 which involves exploiting local privilege escalation opportunities through kernel vulnerabilities. When memory pressure occurs during the rebuild process, the reinsert operation attempts to allocate GFP_ATOMIC memory for inexact policy bins, which can fail due to insufficient resources.
The operational impact of this vulnerability is severe as it leads to system crashes through general protection faults and kernel panics. The error path only issues a WARN_ONCE() message and continues execution rather than properly handling the allocation failure, resulting in poisoned bydst nodes that eventually cause a GPF (General Protection Fault) during subsequent rebuild operations. The crash occurs when hlist_del_rcu() dereferences LIST_POISON2 memory locations, indicating corrupted data structures from the failed allocation.
The fix requires inverting the guard condition so that preallocation covers exactly those policies that will be reinserted, ensuring all necessary hash bins are available before the reinsert loop begins. This prevents the scenario where inexact policy bins must be allocated during reinsertion, which could fail under memory pressure conditions. The vulnerability is deterministic and exploitable through failslab mechanisms, making it particularly dangerous in environments with constrained memory resources.
The root cause demonstrates a classic kernel memory management issue involving resource allocation during critical sections where preallocation should ensure deterministic behavior. When combined with the KASAN (Kernel Address Sanitizer) detection capabilities, this flaw reveals how seemingly minor logic errors in kernel code can lead to catastrophic system failures. The vulnerability affects systems running Linux kernels that implement the xfrm policy framework and represents a significant security concern due to its potential for causing denial of service attacks through carefully crafted memory pressure conditions.