CVE-2026-52943
Received Received - Intake
Use-After-Free in Linux Kernel skbuff

Publication date: 2026-06-24

Last updated on: 2026-06-24

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net: skbuff: fix missing zerocopy reference in pskb_carve helpers pskb_carve_inside_header() and pskb_carve_inside_nonlinear() both copy the old skb_shared_info header into a new buffer via memcpy(), which includes the destructor_arg pointer (uarg) for MSG_ZEROCOPY skbs. Neither function calls net_zcopy_get() for the new shinfo, creating an unaccounted holder: every skb_shared_info with destructor_arg set will call skb_zcopy_clear() once when freed, but the corresponding net_zcopy_get() was never called for the new copy. Repeated calls drive uarg->refcnt to zero prematurely, freeing ubuf_info_msgzc while TX skbs still hold live destructor_arg pointers. KASAN reports use-after-free on a freed ubuf_info_msgzc: BUG: KASAN: slab-use-after-free in skb_release_data+0x77b/0x810 Read of size 8 at addr ffff88801574d3e8 by task poc/220 Call Trace: skb_release_data+0x77b/0x810 kfree_skb_list_reason+0x13e/0x610 skb_release_data+0x4cd/0x810 sk_skb_reason_drop+0xf3/0x340 skb_queue_purge_reason+0x282/0x440 rds_tcp_inc_free+0x1e/0x30 rds_recvmsg+0x354/0x1780 __sys_recvmsg+0xdf/0x180 Allocated by task 219: msg_zerocopy_realloc+0x157/0x7b0 tcp_sendmsg_locked+0x2892/0x3ba0 Freed by task 219: ip_recv_error+0x74a/0xb10 tcp_recvmsg+0x475/0x530 The skb consuming the late access still referenced the same uarg via shinfo->destructor_arg copied by pskb_carve_inside_nonlinear() without a refcount bump. This has been verified to be reliably exploitable: a working proof-of-concept achieves full root privilege escalation from an unprivileged local user on a default kernel configuration. The fix follows the pattern of pskb_expand_head() which has the same memcpy/cloned structure. For pskb_carve_inside_header(), net_zcopy_get() is placed after skb_orphan_frags() succeeds, so the orphan error path needs no cleanup. For pskb_carve_inside_nonlinear(), net_zcopy_get() is placed after all failure points and just before skb_release_data(), so no error path needs cleanup at all -- matching pskb_expand_head() more closely and avoiding the need for a balancing net_zcopy_put().
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Meta Information
Published
2026-06-24
Last Modified
2026-06-24
Generated
2026-06-24
AI Q&A
2026-06-24
EPSS Evaluated
N/A
NVD
CVE-2026-52943
EUVD
EUVD-2026-38732
Affected Vendors & Products
Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *
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Exploitability
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CWE ID Description
CWE-UNKNOWN
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Executive Summary

This vulnerability exists in the Linux kernel's network stack, specifically in the skbuff (socket buffer) handling code. Two functions, pskb_carve_inside_header() and pskb_carve_inside_nonlinear(), copy the skb_shared_info header using memcpy(), which includes a pointer called destructor_arg used for zero-copy message skbs. However, these functions fail to call net_zcopy_get() to increment the reference count for the new copy of the shared info. This leads to a reference count being decremented prematurely, causing the underlying buffer (ubuf_info_msgzc) to be freed while still in use by transmit skbs.

This use-after-free condition is detected by KASAN (Kernel Address Sanitizer) and can be exploited reliably to achieve full root privilege escalation from an unprivileged local user on a default kernel configuration.

Impact Analysis

The vulnerability allows an unprivileged local user to escalate their privileges to full root access on a system running a vulnerable Linux kernel. This means an attacker could gain complete control over the affected system, potentially leading to unauthorized access, data theft, system compromise, and disruption of services.

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