CVE-2026-97524 in Linux
Summary
by MITRE • 09/25/2026
In the Linux kernel, the following vulnerability has been resolved:
mptcp: avoid unneeded actions on subflow reset
Once in a blue moon, the mptcp receive path can recursively call mptcp_data_ready() via state change under unlucky error conditions, and then try to hold the data lock again.
Break the recursion loop explicitly checking for the exceptional condition.
Add a new flag instead of using an existing one like 'closing', to exit early in subflow_state_change(), and explicitly flush the RX queue at reset time.
This avoids unneeded processing to check for available data -- calling get_mapping_status() and more on a dying subflow -- but also in error reporting and worker scheduling.
Note that we must consume the currently peeked skb before invoking mptcp_dss_corruption to avoid consuming it again after the eventual reset has freed it.
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Analysis
by VulDB Data Team • 09/25/2026
The Linux kernel's Multipath TCP implementation contains a logic flaw within its subflow state change handling mechanism that can lead to recursive function calls and unnecessary resource consumption under specific error conditions. The vulnerability centers on the mptcp_data_ready() function, which is responsible for processing incoming data on MPTCP connections. Under unlucky circumstances involving network errors or connection resets, this receive path can trigger a recursive call back into itself via state change notifications. This recursion occurs because the subflow_state_change() routine may invoke callbacks that eventually lead to another invocation of mptcp_data_ready(), creating an unintended loop rather than cleanly terminating the operation on a dying subflow.
This recursive behavior results in redundant processing overhead and potential instability within the kernel network stack. Specifically, when such a recursion occurs, the system attempts to acquire data locks again while they may already be held or in a state that does not support re-entry safely. Furthermore, even if the recursion is avoided through other means, the original code path performs unnecessary checks for available data on subflows that are effectively dead due to reset conditions. These superfluous operations include calling get_mapping_status() and engaging worker scheduling logic, which consume CPU cycles without providing any functional benefit since the connection segment is no longer viable for normal data transmission.
To resolve this issue, developers have introduced a dedicated flag specifically designed to detect and exit early from subflow_state_change() when exceptional conditions are detected. This new flag allows the kernel to bypass the standard processing pipeline that leads to mptcp_data_ready(), thereby breaking the recursion loop explicitly. Additionally, the fix ensures that the receive queue is flushed at reset time, preventing stale data from lingering in buffers associated with closed or resetting subflows. A critical aspect of this patch involves memory management safety; it mandates consuming any currently peeked socket buffer before invoking mptcp_dss_corruption functions. This step prevents double consumption issues where a packet might be freed by the reset process and then inadvertently accessed again, which could lead to use-after-free vulnerabilities or kernel panics.
From a security perspective, this vulnerability aligns with CWE-835, Loop with Unreachable Exit Condition, as it involves an infinite or unintended recursive loop that can degrade system performance. It also relates to CWE-401, Missing Release of Memory after Effective Lifetime, in the context of potential resource leaks if the recursion leads to stack exhaustion or improper buffer handling. In terms of adversary behavior and defensive mapping, this issue falls under MITRE ATT&CK technique T1529, System Shutdown or Reboot, specifically regarding how system stability is maintained during error states, although it is primarily a reliability fix rather than an exploit vector for privilege escalation. The flaw highlights the complexity of maintaining state consistency in concurrent network stacks where multiple callbacks can interact unpredictably under stress conditions.
Mitigation strategies involve applying the upstream kernel patch that introduces the explicit recursion break and proper queue flushing mechanisms. System administrators should ensure their Linux kernels are updated to versions containing this fix, particularly those running MPTCP-enabled configurations which are increasingly common in high-throughput environments like data centers and 5G networks. For organizations unable to immediately update kernels, monitoring for unusual CPU spikes or network stack errors related to MPTCP subflows can serve as an indicator of the vulnerability being triggered under heavy load or adverse network conditions. Regular auditing of kernel logs for recursion warnings or lock contention issues on TCP sockets is recommended to detect potential exploitation attempts that might leverage this instability to cause denial-of-service through resource exhaustion.