{"id":"CVE-2026-99121","title":"ipv4: avoid divide by zero in fib_rebalance","summary":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv4: avoid divide by zero in fib_rebalance\n\nfib_rebalance() computes the total eligible nexthop weight in one pass\nand programs upper bounds in a second pass. A concur…","severity":"none","vendor":"Linux","product":"Linux","affected":["Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f","Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < d5520e815c4b1427104ce1428ee23821f2aa824d","Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < 5046d2880fec7d49ebed2fd2866747ee1d06ad71","Linux 4.4"],"published":"2026-10-28","updated":"2026-10-28","sourceUpdated":"2026-10-28T10:34:37.082Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-99121","references":[{"url":"https://git.kernel.org/stable/c/5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f"},{"url":"https://git.kernel.org/stable/c/d5520e815c4b1427104ce1428ee23821f2aa824d"},{"url":"https://git.kernel.org/stable/c/5046d2880fec7d49ebed2fd2866747ee1d06ad71"}],"tags":["cve.org"],"ingestedAt":"2026-10-28T11:09:40.448Z","slug":"CVE-2026-99121","body":"## Overview\n\nIn the Linux kernel, the following vulnerability has been resolved:\n\nipv4: avoid divide by zero in fib_rebalance\n\nfib_rebalance() computes the total eligible nexthop weight in one pass\nand programs upper bounds in a second pass. A concurrent change to\nignore_routes_with_linkdown can make the first pass return zero while\nthe second pass sees an eligible nexthop, resulting in division by zero.\n\nIf the first pass reports a zero total, set each nexthop upper bound to\n-1 and skip the division. This matches the IPv6 fix in commit\nd2c26c2911dd (\"ipv6: avoid divide by zero in rt6_multipath_rebalance\")\nand preserves the lock-free rebalance path.\n\n## Affected\n\n- `Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f`\n- `Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < d5520e815c4b1427104ce1428ee23821f2aa824d`\n- `Linux >= 0e884c78ee19e902f300ed147083c28a0c6302f0 < 5046d2880fec7d49ebed2fd2866747ee1d06ad71`\n- `Linux 4.4`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":3,"depthScoreParts":{"impact":2.8,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}