{"id":"CVE-2026-99121","state":"PUBLISHED","title":"ipv4: avoid divide by zero in fib_rebalance","description":"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 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.","publishedAt":"2026-10-28T10:34:37.082Z","updatedAt":"2026-10-30T12:41:56.754Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"baf3a767b2845eb8e68f056ee4aa5b41b151e990","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"f655a26490e705ec76a79db7f412847fda342b39","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"7c68f4de5090b17b63b9a0a3b01b3807e01a296a","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"226a974054acbd892560bfa67f0ae8ffe271a736","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"0800c92ca5d1983df6843a5435299978901d1d02","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"d5520e815c4b1427104ce1428ee23821f2aa824d","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"5046d2880fec7d49ebed2fd2866747ee1d06ad71","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fib_semantics.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.4","versionType":"semver"},{"version":"5.10.273","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.224","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.161","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.115","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fib_semantics.c"]}],"references":["https://git.kernel.org/stable/c/baf3a767b2845eb8e68f056ee4aa5b41b151e990","https://git.kernel.org/stable/c/f655a26490e705ec76a79db7f412847fda342b39","https://git.kernel.org/stable/c/7c68f4de5090b17b63b9a0a3b01b3807e01a296a","https://git.kernel.org/stable/c/226a974054acbd892560bfa67f0ae8ffe271a736","https://git.kernel.org/stable/c/0800c92ca5d1983df6843a5435299978901d1d02","https://git.kernel.org/stable/c/5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f","https://git.kernel.org/stable/c/d5520e815c4b1427104ce1428ee23821f2aa824d","https://git.kernel.org/stable/c/5046d2880fec7d49ebed2fd2866747ee1d06ad71"],"weaknesses":[],"ingestedAt":"2026-10-30T13:02:04.640Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/99xxx/CVE-2026-99121.json","commit":"cb14bf1b43b0c9f05f7f40eae2246263fd430780","baselineCommit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-99121","state":"PUBLISHED","datePublished":"2026-10-28T10:34:37.082Z","dateUpdated":"2026-10-30T12:41:56.754Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-25T10:25:14.393Z"},"containers":{"cna":{"title":"ipv4: avoid divide by zero in fib_rebalance","descriptions":[{"lang":"en","value":"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 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."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"baf3a767b2845eb8e68f056ee4aa5b41b151e990","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"f655a26490e705ec76a79db7f412847fda342b39","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"7c68f4de5090b17b63b9a0a3b01b3807e01a296a","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"226a974054acbd892560bfa67f0ae8ffe271a736","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"0800c92ca5d1983df6843a5435299978901d1d02","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"d5520e815c4b1427104ce1428ee23821f2aa824d","versionType":"git"},{"version":"0e884c78ee19e902f300ed147083c28a0c6302f0","status":"affected","lessThan":"5046d2880fec7d49ebed2fd2866747ee1d06ad71","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fib_semantics.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.4","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.4","versionType":"semver"},{"version":"5.10.273","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.224","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.191","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.161","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.115","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.59","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.13","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/ipv4/fib_semantics.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/baf3a767b2845eb8e68f056ee4aa5b41b151e990"},{"url":"https://git.kernel.org/stable/c/f655a26490e705ec76a79db7f412847fda342b39"},{"url":"https://git.kernel.org/stable/c/7c68f4de5090b17b63b9a0a3b01b3807e01a296a"},{"url":"https://git.kernel.org/stable/c/226a974054acbd892560bfa67f0ae8ffe271a736"},{"url":"https://git.kernel.org/stable/c/0800c92ca5d1983df6843a5435299978901d1d02"},{"url":"https://git.kernel.org/stable/c/5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f"},{"url":"https://git.kernel.org/stable/c/d5520e815c4b1427104ce1428ee23821f2aa824d"},{"url":"https://git.kernel.org/stable/c/5046d2880fec7d49ebed2fd2866747ee1d06ad71"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-30T12:41:56.754Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"5.10.273"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"5.15.224"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.1.191"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.6.161"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.12.115"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"6.18.59"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"7.2.13"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.4","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}