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Dismiss alert {{ message }} gregkh / linux Public Notifications You must be signed in to change notification settings Fork 686 Star 644 Code Actions Security and quality 0 Insights Additional navigation options Code Actions Security and quality Insights Commit 6e3b094 Browse files Browse files vanhoefm authored and gregkh committed wifi: prevent A-MSDU attacks in mesh networks commit 737bb91 upstream. This patch is a mitigation to prevent the A-MSDU spoofing vulnerability for mesh networks. The initial update to the IEEE 802.11 standard, in response to the FragAttacks, missed this case ( CVE-2025-27558 ). It can be considered a variant of CVE-2020-24588 but for mesh networks. This patch tries to detect if a standard MSDU was turned into an A-MSDU by an adversary. This is done by parsing a received A-MSDU as a standard MSDU, calculating the length of the Mesh Control header, and seeing if the 6 bytes after this header equal the start of an rfc1042 header. If equal, this is a strong indication of an ongoing attack attempt. This defense was tested with mac80211_hwsim against a mesh network that uses an empty Mesh Address Extension field, i.e., when four addresses are used, and when using a 12-byte Mesh Address Extension field, i.e., when six addresses are used. Functionality of normal MSDUs and A-MSDUs was also tested, and confirmed working, when using both an empty and 12-byte Mesh Address Extension field. It was also tested with mac80211_hwsim that A-MSDU attacks in non-mesh networks keep being detected and prevented. Note that the vulnerability being patched, and the defense being implemented, was also discussed in the following paper and in the following IEEE 802.11 presentation: https://papers.mathyvanhoef.com/wisec2025.pdf https://mentor.ieee.org/802.11/dcn/25/11-25-0949-00-000m-a-msdu-mesh-spoof-protection.docx Cc: stable@vger.kernel.org Signed-off-by: Mathy Vanhoef &lt;Mathy.Vanhoef@kuleuven.be&gt; Link: https://patch.msgid.link/20250616004635.224344-1-Mathy.Vanhoef@kuleuven.be Signed-off-by: Johannes Berg &lt;johannes.berg@intel.com&gt; Signed-off-by: Greg Kroah-Hartman &lt;gregkh@linuxfoundation.org&gt; 1 parent 0ec1ee6 commit 6e3b094 Copy full SHA for 6e3b094 1 file changed + 50 - 2 Lines changed: 50 additions &amp; 2 deletions File tree Expand file tree Collapse file tree Open diff view settings Filter options net/wireless util.c Expand file tree Collapse file tree Open diff view settings Collapse file ‎ net/wireless/util.c ‎ Copy file name to clipboard Expand all lines: net/wireless/util.c + 50 - 2 Lines changed: 50 additions &amp; 2 deletions Original file line number Diff line number Diff line change @@ -820,6 +820,52 @@ bool ieee80211_is_valid_amsdu(struct sk_buff *skb, u8 mesh_hdr) 820 820 } 821 821 EXPORT_SYMBOL ( ieee80211_is_valid_amsdu ); 822 822 823 + 824 + /* 825 + * Detects if an MSDU frame was maliciously converted into an A-MSDU 826 + * frame by an adversary. This is done by parsing the received frame 827 + * as if it were a regular MSDU, even though the A-MSDU flag is set. 828 + * 829 + * For non-mesh interfaces, detection involves checking whether the 830 + * payload, when interpreted as an MSDU, begins with a valid RFC1042 831 + * header. This is done by comparing the A-MSDU subheader&#39;s destination 832 + * address to the start of the RFC1042 header. 833 + * 834 + * For mesh interfaces, the MSDU includes a 6-byte Mesh Control field 835 + * and an optional variable-length Mesh Address Extension field before 836 + * the RFC1042 header. The position of the RFC1042 header must therefore 837 + * be calculated based on the mesh header length. 838 + * 839 + * Since this function intentionally parses an A-MSDU frame as an MSDU, 840 + * it only assumes that the A-MSDU subframe header is present, and 841 + * beyond this it performs its own bounds checks under the assumption 842 + * that the frame is instead parsed as a non-aggregated MSDU. 843 + */ 844 + static bool 845 + is_amsdu_aggregation_attack ( struct ethhdr * eth , struct sk_buff * skb , 846 + enum nl80211_iftype iftype ) 847 + { 848 + int offset ; 849 + 850 + /* Non-mesh case can be directly compared */ 851 + if ( iftype != NL80211_IFTYPE_MESH_POINT ) 852 + return ether_addr_equal ( eth -&gt; h_dest , rfc1042_header ); 853 + 854 + offset = __ieee80211_get_mesh_hdrlen ( eth -&gt; h_dest [ 0 ]); 855 + if ( offset == 6 ) { 856 + /* Mesh case with empty address extension field */ 857 + return ether_addr_equal ( eth -&gt; h_source , rfc1042_header ); 858 + } else if ( offset + ETH_ALEN &lt;= skb -&gt; len ) { 859 + /* Mesh case with non-empty address extension field */ 860 + u8 temp [ ETH_ALEN ]; 861 + 862 + skb_copy_bits ( skb , offset , temp , ETH_ALEN ); 863 + return ether_addr_equal ( temp , rfc1042_header ); 864 + } 865 + 866 + return false; 867 + } 868 + 823 869 void ieee80211_amsdu_to_8023s ( struct sk_buff * skb , struct sk_buff_head * list , 824 870 const u8 * addr , enum nl80211_iftype iftype , 825 871 const unsigned int extra_headroom , @@ -861,8 +907,10 @@ void ieee80211_amsdu_to_8023s(struct sk_buff *skb, struct sk_buff_head *list, 861 907 /* the last MSDU has no padding */ 862 908 if ( subframe_len &gt; remaining ) 863 909 goto purge ; 864 - /* mitigate A-MSDU aggregation injection attacks */ 865 - if ( ether_addr_equal ( hdr . eth . h_dest , rfc1042_header )) 910 + /* mitigate A-MSDU aggregation injection attacks, to be 911 + * checked when processing first subframe (offset == 0). 912 + */ 913 + if ( offset == 0 &amp;&amp; is_amsdu_aggregation_attack ( &amp; hdr . eth , skb , iftype )) 866 914 goto purge ; 867 915 868 916 offset += sizeof ( struct ethhdr ); 0 commit comments Comments 0 ( 0 ) Footer &copy; 2026 GitHub,&nbsp;Inc. 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