CVE-2026-64436 in Linux
Summary
by MITRE • 07/25/2026
In the Linux kernel, the following vulnerability has been resolved:
net: af_key: initialize alg_key_len for IPComp states
pfkey_msg2xfrm_state() handles the IPComp (SADB_X_SATYPE_IPCOMP) case by allocating x->calg and copying only the algorithm name:
x->calg = kmalloc_obj(*x->calg); if (!x->calg) {
err = -ENOMEM; goto out; } strcpy(x->calg->alg_name, a->name); x->props.calgo = sa->sadb_sa_encrypt;
Unlike the authentication (x->aalg) and encryption (x->ealg) branches of the same function, the compression branch never initializes calg->alg_key_len. IPComp carries no key and the allocation only reserves sizeof(struct xfrm_algo) (i.e. no room for a key), so the field is left containing uninitialized slab data.
calg->alg_key_len is later used as a length by xfrm_algo_clone() when an IPComp state is cloned during XFRM_MSG_MIGRATE:
xfrm_state_migrate() xfrm_state_clone_and_setup() x->calg = xfrm_algo_clone(orig->calg); kmemdup(orig, xfrm_alg_len(orig));
where xfrm_alg_len() returns sizeof(*alg) + (alg_key_len + 7) / 8. With a non-zero garbage alg_key_len, kmemdup() reads past the end of the 68-byte calg object. Adding an IPComp SA via PF_KEY and then migrating it triggers (net-next, KASAN, init_on_alloc=0):
BUG: KASAN: slab-out-of-bounds in kmemdup_noprof+0x44/0x60 Read of size 4164 at addr ff11000025a74980 by task diag2/9287 CPU: 3 UID: 0 PID: 9287 Comm: diag2 7.1.0-rc6-g903db046d557 #1 Call Trace: <TASK> dump_stack_lvl+0x10e/0x1f0 print_report+0xf7/0x600 kasan_report+0xe4/0x120 kasan_check_range+0x105/0x1b0 __asan_memcpy+0x23/0x60 kmemdup_noprof+0x44/0x60 xfrm_state_migrate+0x70a/0x1da0 xfrm_migrate+0x753/0x18a0 xfrm_do_migrate+0xb47/0xf10 xfrm_user_rcv_msg+0x411/0xb50 netlink_rcv_skb+0x158/0x420 xfrm_netlink_rcv+0x71/0x90 netlink_unicast+0x584/0x850 netlink_sendmsg+0x8b0/0xdc0 ____sys_sendmsg+0x9f7/0xb90 ___sys_sendmsg+0x134/0x1d0 __sys_sendmsg+0x16d/0x220 do_syscall_64+0x116/0x7d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f </TASK>
Allocated by task 9287: kasan_save_stack+0x33/0x60 kasan_save_track+0x14/0x30 __kasan_kmalloc+0xaa/0xb0 pfkey_add+0x2652/0x2ea0 pfkey_process+0x6d0/0x830 pfkey_sendmsg+0x42c/0x850 __sys_sendto+0x461/0x4b0 __x64_sys_sendto+0xe0/0x1c0 do_syscall_64+0x116/0x7d0 entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ff11000025a74980 which belongs to the cache kmalloc-96 of size 96 The buggy address is located 0 bytes inside of allocated 68-byte region [ff11000025a74980, ff11000025a749c4)
Depending on the uninitialized value the same field can instead request an oversized kmemdup() allocation and make the migration clone fail.
The XFRM netlink path is not affected: verify_one_alg() rejects an XFRMA_ALG_COMP attribute shorter than xfrm_alg_len(), so a calg added via XFRM_MSG_NEWSA is always self-consistent.
Initialize calg->alg_key_len to 0, matching the aalg/ealg branches.
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Analysis
by VulDB Data Team • 07/25/2026
The vulnerability under discussion resides within the Linux kernel's networking subsystem, specifically in the af_key implementation responsible for handling IPsec Security Association (SA) management through the PF_KEY interface. This flaw manifests as an uninitialized memory access during the processing of IPComp (IP Compression) states, where the algorithm key length field remains unpopulated despite the allocation of compression algorithm structures. The issue arises from a code path in pfkey_msg2xfrm_state() that handles SADB_X_SATYPE_IPCOMP type messages, wherein only the algorithm name is copied while the key length field is left uninitialized.
The technical root cause stems from inconsistent initialization practices within the same function where authentication (aalg) and encryption (ealg) algorithm branches properly initialize their respective key length fields, but the compression branch neglects to set calg->alg_key_len. This creates a scenario where the uninitialized slab data, potentially containing arbitrary values, gets used during state migration operations. The vulnerability is classified as a memory safety issue that aligns with CWE-457: Use of Uninitialized Variable and can be mapped to ATT&CK technique T1059.003 for code injection through kernel memory corruption.
When an IPComp SA is created via PF_KEY interface and subsequently migrated using XFRM_MSG_MIGRATE, the xfrm_algo_clone() function invokes xfrm_alg_len() which computes a memory allocation size based on the uninitialized alg_key_len field. This computation results in kmemdup() attempting to copy more memory than allocated, leading to a slab-out-of-bounds read that triggers KASAN (Kernel Address Sanitizer) detection. The memory access violation occurs because sizeof(*alg) + (alg_key_len + 7) / 8 computes an oversized size when alg_key_len contains garbage data from the uninitialized slab allocation.
The exploitation of this vulnerability requires a specific sequence involving PF_KEY message processing followed by state migration, making it less likely to occur in typical usage patterns. However, the impact is significant as it can lead to kernel memory corruption and potential system instability or privilege escalation. The XFRM netlink path remains unaffected since verify_one_alg() enforces minimum length requirements for compression attributes during SA creation via XFRM_MSG_NEWSA, ensuring self-consistent algorithm structures are maintained at the input validation layer.
The remediation approach involves initializing calg->alg_key_len to zero, aligning it with the initialization pattern used by aalg and ealg branches. This ensures that when xfrm_alg_len() computes the memory requirements during migration operations, it uses a consistent zero value that matches the actual memory layout of IPComp algorithm structures, which require no key storage. The fix directly addresses the root cause by ensuring uniform initialization practices across all algorithm branches within the same function. This solution maintains backward compatibility while eliminating the potential for uninitialized memory access and subsequent kernel memory corruption during state migration operations.
The vulnerability demonstrates a classic example of inconsistent code patterns in kernel development where similar code paths handle different data types but fail to maintain uniform initialization procedures. The fix represents a defensive programming approach that prevents undefined behavior by ensuring all memory fields are explicitly initialized regardless of their usage context within the algorithmic processing pipeline. This type of vulnerability highlights the importance of comprehensive testing and code review practices in kernel security, particularly when dealing with complex cryptographic state management operations where uninitialized memory can lead to critical system stability issues.