What’s Vulnerable › Vulnerabilities

CVE-2021-47109: neighbour: allow NUD_NOARP entries to be forced GCed

• Severity: medium (CVSS 5.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2024-03-15 · updated 2026-08-04
• Weakness: CWE-190

Description

In the Linux kernel, the following vulnerability has been resolved: neighbour: allow NUD_NOARP entries to be forced GCed IFF_POINTOPOINT interfaces use NUD_NOARP entries for IPv6. It's possible to fill up the neighbour table with enough entries that it will overflow for valid connections after that. This behaviour is more prevalent after commit 58956317c8de ("neighbor: Improve garbage collection") is applied, as it prevents removal from entries that are not NUD_FAILED, unless they are more than 5s old.

Affected products

• Linux kernel: from 5.0 before 5.4.125; from 5.5 before 5.10.43; from 5.11 before 5.12.10; 5.13-rc1, 5.13-rc2, 5.13-rc3, 5.13-rc4, 5.13-rc5, 5.13-rc6 — fixed in 5.10.43, 5.12.10, 5.4.125

How to fix

Upgrade to a fixed version: Linux kernel 5.10.43, 5.12.10, 5.4.125. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8f
• https://git.kernel.org/stable/c/d17d47da59f726dc4c87caebda3a50333d7e2fd3
• https://git.kernel.org/stable/c/d99029e6aab62aef0a0251588b2867e77e83b137
• https://git.kernel.org/stable/c/ddf088d7aaaaacfc836104f2e632b29b1d383cfc
• https://git.kernel.org/stable/c/7a6b1ab7475fd6478eeaf5c9d1163e7a18125c8f
• https://git.kernel.org/stable/c/d17d47da59f726dc4c87caebda3a50333d7e2fd3
• https://git.kernel.org/stable/c/d99029e6aab62aef0a0251588b2867e77e83b137
• https://git.kernel.org/stable/c/ddf088d7aaaaacfc836104f2e632b29b1d383cfc

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