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CVE-2026-23300

net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop

Published
Last modified
published
Not listed in CISA KEV
Fix
Fixed in 5.10.253, 5.15.203, 6.1.167, 6.6.130, 6.12.77, and 2 more
None on Exploit-DB, Metasploit or GitHub

Summary

In the Linux kernel, the following vulnerability has been resolved: net: ipv6: fix panic when IPv4 route references loopback IPv6 nexthop When a standalone IPv6 nexthop object is created with a loopback device (e.g., "ip -6 nexthop add id 100 dev lo"), fib6_nh_init() misclassifies it as a reject route. This is because nexthop objects have no destination prefix (fc_dst=::), causing fib6_is_reject() to match any loopback nexthop. The reject path skips fib_nh_common_init(), leaving nhc_pcpu_rth_output unallocated. If an IPv4 route later references this nexthop, __mkroute_output() dereferences NULL nhc_pcpu_rth_output and panics. Simplify the check in fib6_nh_init() to only match explicit reject routes (RTF_REJECT) instead of using fib6_is_reject(). The loopback promotion heuristic in fib6_is_reject() is handled separately by ip6_route_info_create_nh(). After this change, the three cases behave as follows: 1. Explicit reject route ("ip -6 route add unreachable 2001:db8::/64"): RTF_REJECT is set, enters reject path, skips fib_nh_common_init(). No behavior change. 2. Implicit loopback reject route ("ip -6 route add 2001:db8::/32 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. ip6_route_info_create_nh() still promotes it to reject afterward. nhc_pcpu_rth_output is allocated but unused, which is harmless. 3. Standalone nexthop object ("ip -6 nexthop add id 100 dev lo"): RTF_REJECT is not set, takes normal path, fib_nh_common_init() is called. nhc_pcpu_rth_output is properly allocated, fixing the crash when IPv4 routes reference this nexthop.

Timeline

  1. CVE published
  2. Record last updated

Affected versions

  • Linux Linux

    From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in 607e68c1b7c5a30c795571be1906d716e989a644; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in c11d7c56c2076ee9cd72004f1976fe0734df2ae9; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in b5062fc2150614c9ea8a611c2e0cb6e047ebfa3a; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in b299121e7453d23faddf464087dff513a495b4fc; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in f7c9f8e3607440fe39300efbaf46cf7b5eecb23f; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in b3b5a037d520afe3d5276e653bc0ff516bbda34c; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in 8650db85b4259d2885d2a80fbc2317ce24194133; From 493ced1ac47c48bb86d9d4e8e87df8592be85a0e · fixed in 21ec92774d1536f71bdc90b0e3d052eff99cf093

  • Linux Linux

    5.3

  • KernelLinux

    From 5.3.0 · fixed in 5.10.253; From 5.11.0 · fixed in 5.15.203; From 5.16.0 · fixed in 6.1.167; From 6.2.0 · fixed in 6.6.130; From 6.7.0 · fixed in 6.12.77; From 6.13.0 · fixed in 6.18.17; From 6.19.0 · fixed in 6.19.7

References 8

git.kernel.org