CVE-2026-63836
batman-adv: tp_meter: avoid divide-by-zero for dec_cwnd
Description
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.
INFO
Published Date :
July 19, 2026, 12:16 p.m.
Last Modified :
July 19, 2026, 12:16 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Affected Products
The following products are affected by CVE-2026-63836
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
Solution
- Update the Linux kernel to resolve the divide-by-zero issue.
- Ensure mss does not exceed 16383 for 32-bit safety.
- Simplify calculation to avoid overflow in divisor.
- Apply the patch for batadv_tp_update_cwnd.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-63836.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-63836 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-63836
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-63836 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-63836 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Jul. 19, 2026
Action Type Old Value New Value Added Affected [{'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': '35264c4d46067d6312871488c810cef387f8c1f6', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': '1381b021bf886b793fa5ffb895a8efae7ba0318f', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': 'd08b69da40a101df1e28bfe1e8fa7a09ffa41107', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': 'cd74176cf1685f35a2e5f212d15748bbfecb53b6', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': 'ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': '7d2a44bc6bbe39aed03c68864aa0e54e04a50278', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': '585616dab0aa9c45bc11b2c8082ca78533bc00e9', 'versionType': 'git'}, {'status': 'affected', 'version': '33a3bb4a3345bb511f9c69c913da95d4693e2a4e', 'lessThan': '33ccd52f3cc9ed46ce395199f89aa3234dc83314', 'versionType': 'git'}], 'programFiles': ['net/batman-adv/tp_meter.c'], 'defaultStatus': 'unaffected'}, {'repo': 'https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git', 'vendor': 'Linux', 'product': 'Linux', 'versions': [{'status': 'affected', 'version': '4.8'}, {'status': 'unaffected', 'version': '0', 'lessThan': '4.8', 'versionType': 'semver'}, {'status': 'unaffected', 'version': '5.10.260', 'versionType': 'semver', 'lessThanOrEqual': '5.10.*'}, {'status': 'unaffected', 'version': '5.15.211', 'versionType': 'semver', 'lessThanOrEqual': '5.15.*'}, {'status': 'unaffected', 'version': '6.1.177', 'versionType': 'semver', 'lessThanOrEqual': '6.1.*'}, {'status': 'unaffected', 'version': '6.6.144', 'versionType': 'semver', 'lessThanOrEqual': '6.6.*'}, {'status': 'unaffected', 'version': '6.12.95', 'versionType': 'semver', 'lessThanOrEqual': '6.12.*'}, {'status': 'unaffected', 'version': '6.18.38', 'versionType': 'semver', 'lessThanOrEqual': '6.18.*'}, {'status': 'unaffected', 'version': '7.1.3', 'versionType': 'semver', 'lessThanOrEqual': '7.1.*'}, {'status': 'unaffected', 'version': '7.2-rc1', 'versionType': 'original_commit_for_fix', 'lessThanOrEqual': '*'}], 'programFiles': ['net/batman-adv/tp_meter.c'], 'defaultStatus': 'affected'}] Added Description 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. Added Reference https://git.kernel.org/stable/c/1381b021bf886b793fa5ffb895a8efae7ba0318f Added Reference https://git.kernel.org/stable/c/33ccd52f3cc9ed46ce395199f89aa3234dc83314 Added Reference https://git.kernel.org/stable/c/35264c4d46067d6312871488c810cef387f8c1f6 Added Reference https://git.kernel.org/stable/c/585616dab0aa9c45bc11b2c8082ca78533bc00e9 Added Reference https://git.kernel.org/stable/c/7d2a44bc6bbe39aed03c68864aa0e54e04a50278 Added Reference https://git.kernel.org/stable/c/ac229c86e49fdb96d91f51bc2fa37a9c4f58c44f Added Reference https://git.kernel.org/stable/c/cd74176cf1685f35a2e5f212d15748bbfecb53b6 Added Reference https://git.kernel.org/stable/c/d08b69da40a101df1e28bfe1e8fa7a09ffa41107