CVE-2026-64538 (GCVE-0-2026-64538)
Vulnerability from cvelistv5
Published
2026-07-27 20:10
Modified
2026-08-17 04:57
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: Fix null-ptr-deref in fib6_nh_mtu_change(). fib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg->dev) and dereferences idev->cnf.mtu6 without a NULL check. addrconf_ifdown() clears dev->ip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has released tb6_lock, so the RA-driven MTU walk can observe a NULL idev and oops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(), but this re-fetch is unguarded; nexthop-backed routes survive addrconf_ifdown()'s flush, so the walk still reaches it after ip6_ptr is nulled. Return 0 when idev is NULL, matching rt6_mtu_change_route() and the fib6_mtu() fix in commit 5ad509c1fdad ("ipv6: Fix null-ptr-deref in fib6_mtu()."). Oops: general protection fault, ... KASAN: null-ptr-deref in range [0x00000000000002a8-0x00000000000002af] RIP: 0010:fib6_nh_mtu_change+0x203/0x990 rt6_mtu_change_route+0x141/0x1d0 __fib6_clean_all+0xd0/0x160 rt6_mtu_change+0xb4/0x100 ndisc_router_discovery+0x24b5/0x2cb0 icmpv6_rcv+0x12e9/0x1710 ipv6_rcv+0x39b/0x410
References
Impacted products
Vendor Product Version
Linux Linux Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
Version: c0b220cf7d80eb8a36ae9f12cae6df4577a6814e
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{
  "containers": {
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          "programFiles": [
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              "version": "0",
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              "versionType": "original_commit_for_fix"
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: Fix null-ptr-deref in fib6_nh_mtu_change().\n\nfib6_nh_mtu_change() re-fetches idev via __in6_dev_get(arg-\u003edev) and\ndereferences idev-\u003ecnf.mtu6 without a NULL check. addrconf_ifdown()\nclears dev-\u003eip6_ptr with RCU_INIT_POINTER() after rt6_disable_ip() has\nreleased tb6_lock, so the RA-driven MTU walk can observe a NULL idev and\noops. The caller rt6_mtu_change_route() guards its own __in6_dev_get(),\nbut this re-fetch is unguarded; nexthop-backed routes survive\naddrconf_ifdown()\u0027s flush, so the walk still reaches it after ip6_ptr is\nnulled.\n\nReturn 0 when idev is NULL, matching rt6_mtu_change_route() and the\nfib6_mtu() fix in commit 5ad509c1fdad (\"ipv6: Fix null-ptr-deref in\nfib6_mtu().\").\n\n  Oops: general protection fault, ... KASAN: null-ptr-deref in range\n        [0x00000000000002a8-0x00000000000002af]\n  RIP: 0010:fib6_nh_mtu_change+0x203/0x990\n   rt6_mtu_change_route+0x141/0x1d0\n   __fib6_clean_all+0xd0/0x160\n   rt6_mtu_change+0xb4/0x100\n   ndisc_router_discovery+0x24b5/0x2cb0\n   icmpv6_rcv+0x12e9/0x1710\n   ipv6_rcv+0x39b/0x410"
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:57:14.474Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/d08d019f2f43a6f9a71e81868bbc326b3afaf37b"
        },
        {
          "url": "https://git.kernel.org/stable/c/1451deca9896957159f0666520a792c1b861af4f"
        },
        {
          "url": "https://git.kernel.org/stable/c/b2c70dd3326809429b709a9c7e9220d29923051a"
        },
        {
          "url": "https://git.kernel.org/stable/c/302d57ed7872838b40e56a868fb4c7da7da606e9"
        },
        {
          "url": "https://git.kernel.org/stable/c/80600b5d0f3ecb9324120dc95b5e915130f516c5"
        },
        {
          "url": "https://git.kernel.org/stable/c/b0d0eb13a0441a8ebf4f227843deaf494f1e2c33"
        },
        {
          "url": "https://git.kernel.org/stable/c/6428634f7a0b7878144b4925c37856bef3224967"
        },
        {
          "url": "https://git.kernel.org/stable/c/46c3b8191aad3d032776bf3bebf03efdf5f4b905"
        }
      ],
      "title": "ipv6: Fix null-ptr-deref in fib6_nh_mtu_change().",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
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  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-64538",
    "datePublished": "2026-07-27T20:10:32.779Z",
    "dateReserved": "2026-07-19T15:36:31.795Z",
    "dateUpdated": "2026-08-17T04:57:14.474Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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