CVE-2025-21960 in Linux
Summary
by MITRE • 04/01/2025
In the Linux kernel, the following vulnerability has been resolved:
eth: bnxt: do not update checksum in bnxt_xdp_build_skb()
The bnxt_rx_pkt() updates ip_summed value at the end if checksum offload is enabled. When the XDP-MB program is attached and it returns XDP_PASS, the bnxt_xdp_build_skb() is called to update skb_shared_info. The main purpose of bnxt_xdp_build_skb() is to update skb_shared_info, but it updates ip_summed value too if checksum offload is enabled. This is actually duplicate work.
When the bnxt_rx_pkt() updates ip_summed value, it checks if ip_summed is CHECKSUM_NONE or not. It means that ip_summed should be CHECKSUM_NONE at this moment. But ip_summed may already be updated to CHECKSUM_UNNECESSARY in the XDP-MB-PASS path. So the by skb_checksum_none_assert() WARNS about it.
This is duplicate work and updating ip_summed in the bnxt_xdp_build_skb() is not needed.
Splat looks like: WARNING: CPU: 3 PID: 5782 at ./include/linux/skbuff.h:5155 bnxt_rx_pkt+0x479b/0x7610 [bnxt_en]
Modules linked in: bnxt_re bnxt_en rdma_ucm rdma_cm iw_cm ib_cm ib_uverbs veth xt_nat xt_tcpudp xt_conntrack nft_chain_nat xt_MASQUERADE nf_] CPU: 3 UID: 0 PID: 5782 Comm: socat Tainted: G W 6.14.0-rc4+ #27 Tainted: [W]=WARN
Hardware name: ASUS System Product Name/PRIME Z690-P D4, BIOS 0603 11/01/2021 RIP: 0010:bnxt_rx_pkt+0x479b/0x7610 [bnxt_en]
Code: 54 24 0c 4c 89 f1 4c 89 ff c1 ea 1f ff d3 0f 1f 00 49 89 c6 48 85 c0 0f 84 4c e5 ff ff 48 89 c7 e8 ca 3d a0 c8 e9 8f f4 ff ff <0f> 0b f RSP: 0018:ffff88881ba09928 EFLAGS: 00010202 RAX: 0000000000000000 RBX: 00000000c7590303 RCX: 0000000000000000 RDX: 1ffff1104e7d1610 RSI: 0000000000000001 RDI: ffff8881c91300b8 RBP: ffff88881ba09b28 R08: ffff888273e8b0d0 R09: ffff888273e8b070 R10: ffff888273e8b010 R11: ffff888278b0f000 R12: ffff888273e8b080 R13: ffff8881c9130e00 R14: ffff8881505d3800 R15: ffff888273e8b000 FS: 00007f5a2e7be080(0000) GS:ffff88881ba00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007fff2e708ff8 CR3: 000000013e3b0000 CR4: 00000000007506f0 PKRU: 55555554 Call Trace: <IRQ> ? __warn+0xcd/0x2f0 ? bnxt_rx_pkt+0x479b/0x7610 ? report_bug+0x326/0x3c0 ? handle_bug+0x53/0xa0 ? exc_invalid_op+0x14/0x50 ? asm_exc_invalid_op+0x16/0x20 ? bnxt_rx_pkt+0x479b/0x7610 ? bnxt_rx_pkt+0x3e41/0x7610 ? __pfx_bnxt_rx_pkt+0x10/0x10 ? napi_complete_done+0x2cf/0x7d0 __bnxt_poll_work+0x4e8/0x1220 ? __pfx___bnxt_poll_work+0x10/0x10 ? __pfx_mark_lock.part.0+0x10/0x10 bnxt_poll_p5+0x36a/0xfa0 ? __pfx_bnxt_poll_p5+0x10/0x10 __napi_poll.constprop.0+0xa0/0x440 net_rx_action+0x899/0xd00 ...
Following ping.py patch adds xdp-mb-pass case. so ping.py is going to be able to reproduce this issue.
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Analysis
by VulDB Data Team • 02/01/2026
The vulnerability described in CVE-2025-21960 affects the Linux kernel's bnxt network driver, specifically within the handling of XDP (eXpress Data Path) programs in the bnxt_xdp_build_skb() function. This issue manifests as an improper update of the ip_summed field during packet processing, leading to a kernel warning and potential operational instability. The root cause lies in the duplication of checksum handling logic between two distinct code paths within the driver's packet reception flow. When an XDP-MB (Multi-Buffer) program is attached and returns XDP_PASS, the bnxt_xdp_build_skb() function is invoked to update skb_shared_info structures. However, this function incorrectly modifies the ip_summed value even when checksum offload is enabled, creating a conflict with the subsequent processing in bnxt_rx_pkt() which already handles this field correctly.
The technical flaw stems from the redundant manipulation of the ip_summed field, which is used to indicate the checksum state of network packets in the Linux kernel's networking stack. The kernel's skb_checksum_none_assert() function is designed to enforce consistency in checksum state management, and when the ip_summed field is modified inappropriately during XDP processing, it triggers a warning because the field has already been updated to CHECKSUM_UNNECESSARY in the XDP-MB-PASS path. This violates the expected state transitions and creates a condition where the kernel's internal consistency checks fail, resulting in the warning message observed in the stack trace. The issue is particularly concerning because it occurs in a critical networking path where performance and reliability are paramount, and the warning indicates a potential for data corruption or incorrect packet processing.
The operational impact of this vulnerability extends beyond mere warnings to potentially affect network performance and system stability. When the kernel generates these warnings, it indicates that the network driver is not properly managing packet metadata, which could lead to incorrect checksum validation decisions or suboptimal packet handling. This is particularly problematic in high-throughput networking environments where the bnxt driver is commonly deployed, as it could cause packet reordering, checksum errors, or even complete packet drops. The vulnerability affects systems running Linux kernel versions that include the bnxt_en driver, particularly those utilizing XDP programs for packet processing. According to CWE classification, this represents a CWE-691: Insufficient Control Flow Management, as the improper handling of control flow during packet processing leads to inconsistent state management. The issue also maps to ATT&CK technique T1059.003: Command and Scripting Interpreter: Windows Command Shell, in the context of kernel-level command execution through network packet processing, though this mapping is more relevant to the broader category of kernel exploitation techniques.
Mitigation strategies for this vulnerability should focus on ensuring that the bnxt_xdp_build_skb() function does not modify the ip_summed field when it is not necessary, as the checksum handling is already properly managed in the main packet processing path. The recommended fix involves removing the ip_summed update operation from the XDP processing code path, allowing the existing bnxt_rx_pkt() function to handle all checksum state management. System administrators should ensure that affected systems are updated with the patched kernel version that resolves this duplicate work issue. Additionally, monitoring for kernel warnings related to ip_summed field modifications can serve as an early detection mechanism for systems that may not have been fully patched. The vulnerability highlights the importance of careful kernel module development practices, particularly in network drivers where multiple code paths interact with shared data structures, and underscores the need for thorough testing of XDP programs in production environments. Organizations should prioritize kernel updates and maintain visibility into their network driver configurations to prevent potential exploitation or performance degradation.