Live › vulnerability › CVE-2026-99121
Go to dashboardA race between a route-rebalance pass and a change to the linkdown route setting can make the Linux kernel divide by zero while handling multipath IPv4 routes. The sources describe a kernel crash (denial of service), not code execution.
Summary written from the sources below. Check the originals before acting.
First seen by InfraStack 2026-10-28 11:32 UTC. All times on this page are UTC.
Systems running a Linux kernel with IPv4 multipath routing, where routes are being changed while traffic flows, are the ones that can hit this path. The sources do not say which configurations use the linkdown setting in practice. Hosts with single-path routing or no multipath routes are less likely to be exposed.
No product ranges from the sources yet.
uname -r and compare against the fixed kernel builds listed by your distribution's advisory for CVE-2026-99121Each row is the first time that source carried this signal. The analyst’s rows are its own findings.
In the Linux kernel, the following vulnerability has been resolved:
ipv4: avoid divide by zero in fib_rebalance
fib_rebalance() computes the total eligible nexthop weight in one pass and programs upper bounds in a second pass. A concurrent change to ignore_routes_with_linkdown can make the first pass return zero while the second pass sees an eligible nexthop, resulting in division by zero.
If the first pass reports a zero total, set each nexthop upper bound to -1 and skip the division. This matches the IPv6 fix in commit d2c26c2911dd ("ipv6: avoid divide by zero in rt6_multipath_rebalance") and preserves the lock-free rebalance path.
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