CVE-2026-99074: Linux Vulnerability

Description

In the Linux kernel, the following vulnerability has been resolved: ipv4: stop PMTU walk when nexthop group shrinks Commit 7d3f3b4367f3 ("net: ipv4: Cache pmtu for all packet paths if multipath enabled") made __ip_rt_update_pmtu() update every path. For nexthop objects, fib_info_num_path() and fib_info_nhc() independently load nh->nh_grp. RCU protects each group's lifetime but does not make the loads observe the same group. If replacement shrinks the group after the loop accepts an index, fib_info_nhc() returns NULL and update_or_create_fnhe() dereferences it. A deterministic probe only widened the existing window between the real operations. On v7.2, an RTM_NEWNEXTHOP replacement published a one-member group after the PMTU reader accepted index 1 from a two-member group, producing: KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: update_or_create_fnhe+0x45/0x15b0 Stop when the indexed path is absent. Groups are dense, so no later index exists in that snapshot. The same real-writer window completed 114,423 PMTU iterations without an oops with this check. A reproducer is available on request. Replacement requires CAP_NET_ADMIN in the network namespace. Where unprivileged user namespaces are permitted, a local user can obtain it in a new user and network namespace.

Metrics

EPSS Probability

0.15%

4.1th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= fc07a232326a623d0be482e307c08ea7049c2846, < 82d83eec893d8ae84f280aec44c60d9fdecc62b5; >= b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e, < a411df69524f91fe3adb8f9544d33e701fc9732c; >= 3bed2abab4a682d426624ce9add9d7b6d475d4e4, < 7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a; >= 7f5005457b3072fe1ddf15bfef869f2a1d98e05e, < c60d17d6dd61adc761ac6f65a008fefbc54cbf87; >= 7d3f3b4367f315a61fc615e3138f3d320da8c466, < c6d670ac656badfd0e15355e07a13a6bdf3b69fd; >= 7d3f3b4367f315a61fc615e3138f3d320da8c466, < f27483f9975b5065ff67054cc7eb8edac6083488; >= 7d3f3b4367f315a61fc615e3138f3d320da8c466, < 6619e01855e65ef35723685a557e3eb106f4ecf5; >= 5.15.179, < 5.15.224; >= 6.1.129, < 6.1.191; >= 6.6.79, < 6.6.160; >= 6.12.16, < 6.12.113
Linux	Linux	6.13

References

Timeline

Published: Oct 23, 2026
Last Modified: Oct 30, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-99074?

In the Linux kernel, the following vulnerability has been resolved: ipv4: stop PMTU walk when nexthop group shrinks Commit 7d3f3b4367f3 ("net: ipv4: Cache pmtu for all packet paths if multipath enabled") made __ip_rt_update_pmtu() update every path. For nexthop objects, fib_info_num_path() and fib_info_nhc() independently load nh->nh_grp. RCU protects each group's lifetime but does not make the loads observe the same group. If replacement shrinks the group after the loop accepts an index, fib_info_nhc() returns NULL and update_or_create_fnhe() dereferences it. A deterministic probe only widened the existing window between the real operations. On v7.2, an RTM_NEWNEXTHOP replacement published a one-member group after the PMTU reader accepted index 1 from a two-member group, producing: KASAN: null-ptr-deref in range [0x0000000000000000-0x0000000000000007] RIP: update_or_create_fnhe+0x45/0x15b0 Stop when the indexed path is absent. Groups are dense, so no later index exists in that snapshot. The same real-writer window completed 114,423 PMTU iterations without an oops with this check. A reproducer is available on request. Replacement requires CAP_NET_ADMIN in the network namespace. Where unprivileged user namespaces are permitted, a local user can obtain it in a new user and network namespace.

How severe is CVE-2026-99074?

Severity scoring for CVE-2026-99074 is pending analysis. The EPSS model estimates a 0.15% probability of exploitation in the next 30 days.

How do I fix CVE-2026-99074?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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