CVE-2026-68302 in Linux
Summary
by MITRE • 08/10/2026
In the Linux kernel, the following vulnerability has been resolved:
amt: re-read skb header pointers after every pull
Several AMT receive and transmit paths cache a pointer into the skb head (ip_hdr(), ipv6_hdr(), eth_hdr() or the AMT message header) and then call a helper that can reallocate that head before the cached pointer is used again. pskb_may_pull(), ip_mc_may_pull(), ipv6_mc_may_pull(), iptunnel_pull_header(), ip_mc_check_igmp() and ipv6_mc_check_mld() can all free the old head and move the data, so a pointer taken before the call dangles afterwards and the later access is a use-after-free of the freed head.
The affected sites are:
amt_rcv() caches ip_hdr() before amt_parse_type() pulls, then reads iph->saddr.
amt_dev_xmit() caches ip_hdr()/ipv6_hdr() before ip_mc_check_igmp()/ ipv6_mc_check_mld() and pskb_may_pull(), then reads the group address.
amt_multicast_data_handler() caches eth_hdr() before pskb_may_pull(), then writes the L2 header.
amt_membership_query_handler() caches the AMT header, the outer and inner eth_hdr() and ip_hdr() before iptunnel_pull_header() and several pulls, then reads and writes them.
amt_igmpv3_report_handler() and amt_mldv2_report_handler() cache ip_hdr()/ipv6_hdr() and the current group record and read the record count from the report header inside the record loop, across the *_mc_may_pull() calls.
amt_update_handler() caches ip_hdr() and the AMT membership-update header before pskb_may_pull(), iptunnel_pull_header(), ip_mc_check_igmp() and the report handler, then reads iph->daddr and amtmu->nonce / amtmu->response_mac.
Fix each site by either snapshotting the scalar that is used after the pull before the first pull runs, or re-deriving the header pointer from the skb after the last pull that can move the head. Values that are stable across the pull (source and group address, the response MAC and nonce, the record count, the outer source MAC) are snapshotted; pointers that are written through or read repeatedly are re-derived.
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Analysis
by VulDB Data Team • 08/10/2026
The vulnerability described represents a critical use-after-free condition in the Linux kernel's AMT (Apple Mac Tunnel) implementation that arises from improper handling of socket buffer (skb) header pointer management during network packet processing. This flaw occurs when network drivers cache pointers to IP, IPv6, or Ethernet headers before invoking functions that may reallocate the underlying packet data structure, creating a scenario where cached pointers become invalid after memory reallocation operations. The vulnerability stems from fundamental issues in how kernel network subsystems manage memory reorganization during packet processing, particularly in multicast and tunneling contexts where packet headers must be manipulated and validated.
The technical implementation flaw manifests through several specific code paths where header pointers are cached without proper synchronization with potential memory reallocations that occur during packet processing. Functions such as pskb_may_pull(), ip_mc_may_pull(), ipv6_mc_may_pull(), iptunnel_pull_header(), ip_mc_check_igmp() and ipv6_mc_check_mld() all have the capability to free the original skb head and relocate packet data, causing cached pointers to become dangling references. This pattern violates fundamental memory safety principles and creates predictable attack vectors for privilege escalation or denial-of-service conditions. The vulnerability directly maps to CWE-416 (Use After Free) and CWE-125 (Out-of-bounds Read) categories within the Common Weakness Enumeration framework, representing a classic memory management error where program state becomes inconsistent due to improper pointer invalidation handling.
Operational impact of this vulnerability extends across multiple network processing pathways including multicast packet reception, tunneling operations, and group membership management. The affected functions process AMT packets through various kernel subsystems including multicast routing, IGMP (Internet Group Management Protocol), and MLD (Multicast Listener Discovery) handling, making the exploitation potential widespread across different network topologies and applications. Attackers could leverage this vulnerability to execute arbitrary code with kernel privileges by manipulating packet data structures in ways that trigger the use-after-free conditions during normal network processing operations. The severity is amplified because these paths are frequently traversed in active network environments where multicast traffic and tunneling operations occur regularly, providing attackers with consistent opportunities for exploitation.
Mitigation strategies focus on implementing proper pointer validation and re-initialization patterns before and after memory allocation operations that may relocate packet data. The recommended approach involves either snapshotting scalar values such as addresses and counters that remain stable across memory reallocations, or re-deriving header pointers from the updated skb structure after each pull operation completes. This solution pattern aligns with established kernel security practices for handling dynamic memory operations in network subsystems and follows ATT&CK technique T1068 (Local Port Knocking) by preventing exploitation of memory corruption vulnerabilities through proper defensive programming. The fix implementation requires careful code review and modification across all identified vulnerable functions to ensure that header pointers are properly refreshed after any potential memory reallocation, thereby maintaining consistency between cached references and actual packet data locations while preserving functional correctness of network processing operations.