CVE-2026-72057 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
net/sched: act_ct: preserve tc_skb_cb across defragmentation
tcf_ct_handle_fragments() calls nf_ct_handle_fragments() without saving and restoring skb->cb. The defrag helper clears IPCB/IP6CB, which aliases the tc_skb_cb/qdisc_skb_cb control buffer. Fragmented traffic through act_ct therefore loses qdisc metadata such as pkt_segs and can trigger WARN_ON_ONCE() in qdisc_pkt_segs() when panic_on_warn is enabled.
Save and restore the full tc_skb_cb around nf_ct_handle_fragments(), matching the pattern used by ovs_ct_handle_fragments().
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides in the Linux kernel's net/sched subsystem within the act_ct (connection tracking) action implementation. This flaw specifically affects how fragmented network packets are processed when connection tracking is applied, creating a critical metadata corruption issue that can lead to system instability and potential denial of service conditions.
The technical root cause involves the tcf_ct_handle_fragments() function which invokes nf_ct_handle_fragments() without properly preserving the tc_skb_cb (traffic control socket control buffer) context. This oversight occurs because the defragmentation helper function clears IPCB/IP6CB fields that are aliased with the tc_skb_cb/qdisc_skb_cb control buffers. When fragmented packets pass through the connection tracking action, essential qdisc metadata including pkt_segs information becomes corrupted or lost during the defragmentation process.
The operational impact of this vulnerability manifests when panic_on_warn is enabled in kernel configuration, where the corruption of qdisc metadata triggers WARN_ON_ONCE() assertions within qdisc_pkt_segs() function. This condition can cause unexpected system panics and crashes, particularly in environments handling high volumes of fragmented network traffic with connection tracking enabled. The issue affects network performance and system stability, potentially leading to complete service disruption in production environments.
This vulnerability aligns with CWE-1216 which addresses improper preservation of control buffer data during packet processing operations. The flaw demonstrates a pattern common in kernel networking subsystems where inter-module dependencies are not properly managed across different packet handling contexts. The recommended mitigation strategy involves implementing proper tc_skb_cb preservation around the nf_ct_handle_fragments() call, following the established pattern used by ovs_ct_handle_fragments() implementation. This approach ensures that all qdisc metadata remains intact during connection tracking operations, maintaining system stability and preventing potential exploitation through controlled denial of service attacks.
The fix addresses a fundamental issue in kernel packet processing where buffer context management fails to account for shared memory regions between different subsystems. By saving and restoring the complete tc_skb_cb structure, the implementation maintains data integrity across module boundaries while preserving all necessary qdisc metadata required for proper network queue management and packet handling operations. This solution follows established kernel development practices for maintaining consistency in packet metadata handling throughout complex networking workflows.