CVE-2026-46306
Received Received - Intake
Flow dissector DoS in Linux kernel

Publication date: 2026-06-08

Last updated on: 2026-06-08

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: flow_dissector: do not dissect PPPoE PFC frames RFC 2516 Section 7 states that Protocol Field Compression (PFC) is NOT RECOMMENDED for PPPoE. In practice, pppd does not support negotiating PFC for PPPoE sessions, and the flow dissector driver has assumed an uncompressed frame until the blamed commit. During the review process of that commit [1], support for PFC is suggested. However, having a compressed (1-byte) protocol field means the subsequent PPP payload is shifted by one byte, causing 4-byte misalignment for the network header and an unaligned access exception on some architectures. The exception can be reproduced by sending a PPPoE PFC frame to an ethernet interface of a MIPS board, with RPS enabled, even if no PPPoE session is active on that interface: $ 0 : 00000000 80c40000 00000000 85144817 $ 4 : 00000008 00000100 80a75758 81dc9bb8 $ 8 : 00000010 8087ae2c 0000003d 00000000 $12 : 000000e0 00000039 00000000 00000000 $16 : 85043240 80a75758 81dc9bb8 00006488 $20 : 0000002f 00000007 85144810 80a70000 $24 : 81d1bda0 00000000 $28 : 81dc8000 81dc9aa8 00000000 805ead08 Hi : 00009d51 Lo : 2163358a epc : 805e91f0 __skb_flow_dissect+0x1b0/0x1b50 ra : 805ead08 __skb_get_hash_net+0x74/0x12c Status: 11000403 KERNEL EXL IE Cause : 40800010 (ExcCode 04) BadVA : 85144817 PrId : 0001992f (MIPS 1004Kc) Call Trace: [<805e91f0>] __skb_flow_dissect+0x1b0/0x1b50 [<805ead08>] __skb_get_hash_net+0x74/0x12c [<805ef330>] get_rps_cpu+0x1b8/0x3fc [<805fca70>] netif_receive_skb_list_internal+0x324/0x364 [<805fd120>] napi_complete_done+0x68/0x2a4 [<8058de5c>] mtk_napi_rx+0x228/0xfec [<805fd398>] __napi_poll+0x3c/0x1c4 [<805fd754>] napi_threaded_poll_loop+0x234/0x29c [<805fd848>] napi_threaded_poll+0x8c/0xb0 [<80053544>] kthread+0x104/0x12c [<80002bd8>] ret_from_kernel_thread+0x14/0x1c Code: 02d51821 1060045b 00000000 <8c640000> 3084000f 2c820005 144001a2 00042080 8e220000 To reduce the attack surface and maintain performance, do not process PPPoE PFC frames. [1] https://lore.kernel.org/r/[email protected]
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Meta Information
Published
2026-06-08
Last Modified
2026-06-08
Generated
2026-06-09
AI Q&A
2026-06-08
EPSS Evaluated
N/A
NVD
CVE-2026-46306
EUVD
EUVD-2026-35171
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
linux linux_kernel *
linux_kernel 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 flow dissector component related to PPPoE (Point-to-Point Protocol over Ethernet) frames that use Protocol Field Compression (PFC). According to RFC 2516 Section 7, PFC is not recommended for PPPoE, and the PPP daemon (pppd) does not support negotiating PFC for PPPoE sessions.

The vulnerability arises because the flow dissector driver assumed PPPoE frames were uncompressed until a recent commit suggested supporting PFC. However, compressed protocol fields shift the PPP payload by one byte, causing a 4-byte misalignment in the network header. This misalignment can trigger unaligned access exceptions on some CPU architectures, such as MIPS.

An attacker can reproduce this exception by sending a PPPoE PFC frame to an Ethernet interface on a MIPS board with RPS (Receive Packet Steering) enabled, even if no PPPoE session is active on that interface. This can cause kernel exceptions and potentially disrupt normal operation.

The fix involves not processing PPPoE PFC frames to reduce the attack surface and maintain performance.

Impact Analysis

This vulnerability can cause unaligned access exceptions on affected systems, particularly on architectures like MIPS. Such exceptions can lead to kernel crashes or instability, potentially resulting in denial of service conditions.

Since the vulnerability can be triggered by sending specially crafted PPPoE PFC frames to an Ethernet interface, an attacker with network access could exploit this to disrupt network services or cause system instability.

Detection Guidance

This vulnerability can be detected by observing unaligned access exceptions or kernel crashes on affected architectures such as MIPS when PPPoE PFC frames are received. Specifically, the exception can be reproduced by sending a PPPoE PFC frame to an ethernet interface with RPS enabled, even if no PPPoE session is active.

A sample command to reproduce the issue involves sending a PPPoE PFC frame to the interface, but no explicit detection commands are provided in the available information.

Monitoring kernel logs for messages related to __skb_flow_dissect or __skb_get_hash_net failures and unaligned access exceptions on MIPS architectures may help detect the vulnerability in action.

Mitigation Strategies

To mitigate this vulnerability, the recommended immediate step is to avoid processing PPPoE Protocol Field Compression (PFC) frames in the flow dissector driver.

Since RFC 2516 Section 7 states that PFC is not recommended for PPPoE and pppd does not support negotiating PFC, disabling or not supporting PPPoE PFC frames reduces the attack surface and prevents the unaligned access exception.

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