CVE-2026-63836

CVE CVE-2026-63836EUVD EUVD-2026-45502Published 2026-07-19T12:02:27.000Z

What the advisory describes

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.

Source: EUVD (ENISA), in the words of the advisory.

Products the advisory names

These come from the advisory itself, not from any check we performed.

• Linux — Linux 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <33ccd52f3cc9ed46ce395199f89aa3234dc83314; patch: 7.1.3; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <35264c4d46067d6312871488c810cef387f8c1f6; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <585616dab0aa9c45bc11b2c8082ca78533bc00e9; patch: 5.15.211; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <7d2a44bc6bbe39aed03c68864aa0e54e04a50278; 4.8; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <d08b69da40a101df1e28bfe1e8fa7a09ffa41107; patch: 6.12.95; patch: 5.10.260; patch: 6.18.38; patch: 0; patch: 6.6.144; patch: 6.1.177; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <cd74176cf1685f35a2e5f212d15748bbfecb53b6; patch: 7.2-rc1; 33a3bb4a3345bb511f9c69c913da95d4693e2a4e <1381b021bf886b793fa5ffb895a8efae7ba0318f

The versions shown are the advisory's own. Patchlage compares no version numbers and derives no judgement from them — which version is installed is something a person has to look up.

Carried in the product catalogue

An estate covering these products can be recorded in Patchlage. An advisory about them appears in the next morning's situation report.

• Linux — Linux

Patchlage reports hits and suspected hits. About everything else this system says nothing — neither this page nor the situation report ever claims that an estate is safe.