VulnerabilityPublished 28 Oct 2026

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

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in d5520e815c4b1427104ce1428ee23821f2aa824d : update Linux kernel when convenient.

Data as of 28 Oct 2026, 10:58 UTC

Severity

Unrated

Rated by Threat Radar · CVSS not yet scored by NVD

Patch: Available – fixed in d5520e815c4b1427104ce1428ee23821f2aa824d, 5046d2880fec7d49ebed2fd2866747ee1d06ad71, 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f

Exploitation evidence

Disclosed: evidence found.
CVE published 28 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade Linux kernel to d5520e815c4b1427104ce1428ee23821f2aa824d, 5046d2880fec7d49ebed2fd2866747ee1d06ad71 or 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 0e884c78ee19e902f300ed147083c28a0c6302f0, < d5520e815c4b1427104ce1428ee23821f2aa824d	Fixed in d5520e815c4b1427104ce1428ee23821f2aa824d
LinuxLinux	Affected ≥ 0e884c78ee19e902f300ed147083c28a0c6302f0, < 5046d2880fec7d49ebed2fd2866747ee1d06ad71	Fixed in 5046d2880fec7d49ebed2fd2866747ee1d06ad71
LinuxLinux	Affected ≥ 0e884c78ee19e902f300ed147083c28a0c6302f0, < 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f	Fixed in 5dac5c7ba8f5f3fb4bf29f2a2c3cb552f5b83c8f
LinuxLinux	Affected =4.4	Fixed in–

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.

References

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