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National Vulnerability Database

National Vulnerability Database

NVD

National Vulnerability Database
  1. Vulnerabilities

CVE-2026-74656 Detail

Description

In the Linux kernel, the following vulnerability has been resolved: ipv4: fix use-after-free in fib_nhc_update_mtu() fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses rcu_dereference_protected() with a constant true condition without holding fnhe_lock. The following interleaving can therefore occur: CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access fnhe after grace period KASAN reported: BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410 fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120 The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a mixed pair. Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps the current entry alive while the short critical section serializes its paired PMTU fields. This avoids holding the global lock while scanning all 2048 buckets for every nexthop.


Metrics

 
NVD enrichment efforts reference publicly available information to associate vector strings. CVSS information contributed by other sources is also displayed.
CVSS 4.0 Severity and Vector Strings:

NIST CVSS score
NIST: NVD
N/A
NVD assessment not yet provided.

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URL Source(s) Tag(s)
https://git.kernel.org/stable/c/5a28a4b22dde92f9d293b94236314b8d6181dc4a kernel.org
https://git.kernel.org/stable/c/63996ffc594d128ccec8fc0983f91effd2d3adc4 kernel.org
https://git.kernel.org/stable/c/bc5bde9ce3cc36502839dfe98e068f7303a50982 kernel.org
https://git.kernel.org/stable/c/dfe388da13aa784851e5ebbea90afbb099075761 kernel.org
https://git.kernel.org/stable/c/e00f7d2b5f2540a3415a229c982af7a25ff6362e kernel.org
https://git.kernel.org/stable/c/e1e602d6b22d5cb1641c4459c487eb18bf569e0a kernel.org
https://git.kernel.org/stable/c/ed503eaad62f20cdd5122d7c3078a648a99c8f16 kernel.org
https://git.kernel.org/stable/c/fd39e711866498ae94fcf9acf6f422a4f045b681 kernel.org

Weakness Enumeration

CWE-ID CWE Name Source

Change History

1 change records found show changes

Quick Info

CVE Dictionary Entry:
CVE-2026-74656
NVD Published Date:
08/22/2026
NVD Last Modified:
08/22/2026
Source:
kernel.org