{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:11",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.12.105-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "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(\u0026fnhe_lock)                                        fnhe_remove_oldest()                                          unlink fnhe                                          kfree_rcu(fnhe, rcu)     \u003cquiescent state\u003e     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.",
  "id": "DEBIAN-CVE-2026-74656",
  "modified": "2026-08-27T08:48:05.025331455Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-74656"
    }
  ],
  "upstream": [
    "CVE-2026-74656"
  ]
}