CVE-2026-63968: ipv6: fix possible infinite loop in fib6_select_path()

Severity: high (CVSS 7.5 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: 2026-07-19 · updated 2026-10-30
Weakness: CWE-835

Description

In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible infinite loop in fib6_select_path() Found while auditing the same pattern Sashiko reported in rt6_fill_node() [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings) without waiting for RCU readers; first->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &first->fib6_siblings as its terminator. fib6_purge_rt() always WRITE_ONCE()s first->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev

Affected products

Linux kernel: from 6.1.128 before 6.1.176; from 6.6.75 before 6.6.143; from 6.11.11 before 6.12; from 6.12.2 before 6.12.93; from 6.13 before 6.18.35; from 6.19 before 7.0.12 — fixed in 6.1.176, 6.6.143, 6.12, 6.12.93, 6.18.35, 7.0.12
Linux kernel: from 6.1.128 before 6.1.176; from 6.6.75 before 6.6.143; from 6.12.2 before 6.12.93; from 6.11.11 before 6.12; 6.13 — fixed in 6.1.176, 6.12, 6.12.93, 6.6.143, 7.1

How to fix

Upgrade to a fixed version: Linux kernel 6.1.176, 6.6.143, 6.12, 6.12.93; Linux kernel 6.1.176, 6.12, 6.12.93, 6.6.143. Check the vendor advisory for mitigations.

References

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