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Vulnerability · Published Oct 28, 2026 · Assigned by Linux

CVE-2026-99121ipv4: avoid divide by zero in fib_rebalance

Unrated

In plain English

A security flaw in Linux from Linux. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 8% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS )–Not rated
Exploit odds (30 days)0.2%top 91.8% of all CVEs
Exploited in the wildNo reportsnot in CISA KEV
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12linuxno fix listedDEBIAN-CVE-2026-99121
Debian:13linux6.12.115-2DEBIAN-CVE-2026-99121
Debian:14linux7.2.13-1DEBIAN-CVE-2026-99121
Ubuntu:22.04:LTSlinuxno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinuxno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinuxno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-allwinner-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-awsno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-awsno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-awsno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-aws-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-aws-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-aws-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-aws-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-aws-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-aws-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-aws-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azureno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azureno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-azureno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-fdeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-fdeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-azure-fdeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-fde-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-fde-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-fde-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-fde-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-azure-fde-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-fde-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-nvidiano fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-azure-nvidia-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gcpno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gcpno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-gcpno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gcp-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gcp-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gcp-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gcp-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gcp-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gcp-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gcp-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gcp-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gkeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gkeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-gkeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-gkeopno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-gkeopno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-hwe-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-hwe-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-hwe-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-hwe-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-hwe-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-hwe-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-hwe-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-hwe-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-ibmno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-ibmno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-ibmno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-ibm-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-intel-iot-realtimeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-intel-iotgno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-kvmno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-lowlatencyno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-lowlatencyno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-lowlatency-hwe-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-lowlatency-hwe-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-lowlatency-hwe-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-lowlatency-hwe-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-lowlatency-hwe-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidiano fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidiano fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-nvidiano fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidia-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidia-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidia-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidia-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidia-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidia-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-nvidia-bosno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidia-lowlatencyno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidia-tegrano fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-nvidia-tegrano fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-nvidia-tegra-igxno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oem-5.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oem-6.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oem-6.1no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oem-6.11no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oem-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oem-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oem-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oem-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-oem-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oracleno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oracleno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-oracleno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oracle-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oracle-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oracle-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-oracle-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-oracle-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-raspino fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-raspino fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-raspino fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-raspi-realtimeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-realtimeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-realtimeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-realtimeno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-riscvno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-riscvno fix listedUBUNTU-CVE-2026-99121
Ubuntu:26.04:LTSlinux-riscvno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-riscv-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-riscv-6.14no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-riscv-6.17no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-riscv-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-riscv-6.8no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-riscv-7.0no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-starfive-5.19no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-starfive-6.2no fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-starfive-6.5no fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-vmwareno fix listedUBUNTU-CVE-2026-99121
Ubuntu:24.04:LTSlinux-xilinxno fix listedUBUNTU-CVE-2026-99121
Ubuntu:22.04:LTSlinux-xilinx-zynqmpno fix listedUBUNTU-CVE-2026-99121

Affected products (as reported)

VendorProductVersions
Linux Linux 0e884c78ee19e902f300ed147083c28a0c6302f0 – before baf3a767b2845eb8e68f056ee4aa5b41b151e9900e884c78ee19e902f300ed147083c28a0c6302f0 – before f655a26490e705ec76a79db7f412847fda342b390e884c78ee19e902f300ed147083c28a0c6302f0 – before 7c68f4de5090b17b63b9a0a3b01b3807e01a296a0e884c78ee19e902f300ed147083c28a0c6302f0 – before 226a974054acbd892560bfa67f0ae8ffe271a7360e884c78ee19e902f300ed147083c28a0c6302f0 – before 0800c92ca5d1983df6843a5435299978901d1d020e884c78ee19e902f300ed147083c28a0c6302f0 – before 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f0e884c78ee19e902f300ed147083c28a0c6302f0 – before d5520e815c4b1427104ce1428ee23821f2aa824d0e884c78ee19e902f300ed147083c28a0c6302f0 – before 5046d2880fec7d49ebed2fd2866747ee1d06ad71
Linux Linux 4.4

References