CVE-2026-63836
Low risk· EPSS 7%Exploitation Probability (EPSS)
Low risk7th percentile - higher than 7% of all known CVEs
Summary
In the Linux kernel, the batman-adv tp_meter module has a divide-by-zero vulnerability in batadv_tp_update_cwnd() due to 32-bit arithmetic overflow when cwnd reaches 0x20000000, causing a division by zero.
Risk Assessment
An attacker can remotely trigger a divide-by-zero, leading to kernel panic or denial of service (DoS) on systems using BATMAN-Advanced protocol.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit simplifying cwnd calculation). Apply the security patch promptly in production environments.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: batman-adv: tp_meter: avoid divide-by-zero for dec_cwnd The cwnd is always MSS <= cwnd <= 0x20000000. But the calculation in batadv_tp_update_cwnd() assumes unsigned 32 bit arithmetics. ((mss * 8) ** 2) / (cwnd * 8) In case cwnd is actually 0x20000000, it will be shifted by 3 bit to the left end up at 0x100000000 or U32_MAX + 1. It will therefore wrap around and be 0 - resulting in: ((mss * 8) ** 2) / 0 This is of course invalid and cannot be calculated. The calculation should must be simplified to avoid this overflow: (mss ** 2) * 8 / cwnd It will keep the precision enhancement from the scaling (by 8) but avoid the overflow in the divisor. In theory, there could still be an overflow in the dividend. It is at the moment fixed to BATADV_TP_PLEN in batadv_tp_recv_ack() - so it is not an imminent problem. But allowing it to use the whole u32 bit range, would mean that it can still use up to 67 bits. To keep this calculation safe for 32 bit arithmetic, mss must never use more than floor((32 - 3) / 2) bits - or in other words: must never be larger than 16383.