CVE-2026-99074 is a vulnerability in Linux Kernel
Published on October 23, 2026
ipv4: stop PMTU walk when nexthop group shrinks
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.
Products Associated with CVE-2026-99074
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Affected Versions
Linux:- Version 3bed2abab4a682d426624ce9add9d7b6d475d4e4 and below 7fd60d3c9a1e1b11ef5f1643bbae78d91eae2f4a is affected.
- Version 7f5005457b3072fe1ddf15bfef869f2a1d98e05e and below c60d17d6dd61adc761ac6f65a008fefbc54cbf87 is affected.
- Version 7d3f3b4367f315a61fc615e3138f3d320da8c466 and below c6d670ac656badfd0e15355e07a13a6bdf3b69fd is affected.
- Version 7d3f3b4367f315a61fc615e3138f3d320da8c466 and below f27483f9975b5065ff67054cc7eb8edac6083488 is affected.
- Version 7d3f3b4367f315a61fc615e3138f3d320da8c466 and below 6619e01855e65ef35723685a557e3eb106f4ecf5 is affected.
- Version fc07a232326a623d0be482e307c08ea7049c2846 is affected.
- Version b1f7bdee5750d6cbb9497140cd6582abc5fdcb9e is affected.
- Version 6.6.79 and below 6.6.160 is affected.
- Version 6.12.16 and below 6.12.113 is affected.
- Version 5.15.179 and below 5.16 is affected.
- Version 6.1.129 and below 6.2 is affected.
- Version 6.13 is affected.
- Before 6.13 is unaffected.
- Version 6.6.160, <= 6.6.* is unaffected.
- Version 6.12.113, <= 6.12.* is unaffected.
- Version 6.18.57, <= 6.18.* is unaffected.
- Version 7.2.11, <= 7.2.* is unaffected.
- Version 7.3, <= * is unaffected.