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vuln-cve/data/2026/52xxx/CVE-2026-52943.json
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"cveId": "CVE-2026-52943",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skbuff: fix missing zerocopy reference in pskb_carve helpers\n\npskb_carve_inside_header() and pskb_carve_inside_nonlinear() both copy\nthe old skb_shared_info header into a new buffer via memcpy(), which\nincludes the destructor_arg pointer (uarg) for MSG_ZEROCOPY skbs.\nNeither function calls net_zcopy_get() for the new shinfo, creating an\nunaccounted holder: every skb_shared_info with destructor_arg set will\ncall skb_zcopy_clear() once when freed, but the corresponding\nnet_zcopy_get() was never called for the new copy. Repeated calls\ndrive uarg->refcnt to zero prematurely, freeing ubuf_info_msgzc while\nTX skbs still hold live destructor_arg pointers.\n\nKASAN reports use-after-free on a freed ubuf_info_msgzc:\n\n BUG: KASAN: slab-use-after-free in skb_release_data+0x77b/0x810\n Read of size 8 at addr ffff88801574d3e8 by task poc/220\n\n Call Trace:\n skb_release_data+0x77b/0x810\n kfree_skb_list_reason+0x13e/0x610\n skb_release_data+0x4cd/0x810\n sk_skb_reason_drop+0xf3/0x340\n skb_queue_purge_reason+0x282/0x440\n rds_tcp_inc_free+0x1e/0x30\n rds_recvmsg+0x354/0x1780\n __sys_recvmsg+0xdf/0x180\n\n Allocated by task 219:\n msg_zerocopy_realloc+0x157/0x7b0\n tcp_sendmsg_locked+0x2892/0x3ba0\n\n Freed by task 219:\n ip_recv_error+0x74a/0xb10\n tcp_recvmsg+0x475/0x530\n\nThe skb consuming the late access still referenced the same uarg via\nshinfo->destructor_arg copied by pskb_carve_inside_nonlinear() without\na refcount bump. This has been verified to be reliably exploitable: a\nworking proof-of-concept achieves full root privilege escalation from\nan unprivileged local user on a default kernel configuration.\n\nThe fix follows the pattern of pskb_expand_head() which has the same\nmemcpy/cloned structure. For pskb_carve_inside_header(), net_zcopy_get()\nis placed after skb_orphan_frags() succeeds, so the orphan error path\nneeds no cleanup. For pskb_carve_inside_nonlinear(), net_zcopy_get() is\nplaced after all failure points and just before skb_release_data(), so\nno error path needs cleanup at all -- matching pskb_expand_head() more\nclosely and avoiding the need for a balancing net_zcopy_put()."
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"value": "AV:L - The vulnerable zerocopy state is created by a local process using TCP MSG_ZEROCOPY; remote RDS/TCP packets can reach pskb_extract() but do not carry local ubuf_info destructor_arg state. A local unprivileged attacker can connect to the in-kernel RDS/TCP listener and send crafted zerocopy TCP data.\nAC:L - The fix commit states the issue is reliably exploitable with a working proof-of-concept, and the trigger is a deterministic missing reference count rather than an attacker-uncontrolled race. The attacker controls the local TCP connection, message layout, zerocopy sends, and repeated triggering.\nPR:L - The attack requires the ability to run local unprivileged code and create ordinary TCP sockets with SO_ZEROCOPY/MSG_ZEROCOPY, which has no capability check. No real root or init-namespace administrative privilege is required.\nUI:N - No victim user action is required once the local attacker runs the exploit. The attacker directly drives the socket operations and RDS/TCP receive path.\nS:U - The vulnerability is exploited within the kernel and impacts the same kernel security authority. It is a standard local kernel privilege escalation, not a VM escape or cross-scope boundary violation.\nC:H - This is a use-after-free of ubuf_info_msgzc reachable through skb zerocopy cleanup, and the fix commit confirms a working full root privilege-escalation exploit. Such kernel UAF exploitation can provide access to protected kernel and process memory.\nI:H - The stale ubuf_info pointer is later dereferenced through zerocopy completion handling, giving a memory-corruption primitive suitable for control-flow or credential manipulation. The reported exploit achieves full root privilege escalation.\nA:H - The bug produces a KASAN-confirmed slab use-after-free in skb_release_data() and can crash the kernel during skb cleanup. Even without full exploitation, repeated triggering can cause kernel oops/panic-level denial of service."
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