GHSA-MHMM-JQVJ-99W7

Vulnerability from github – Published: 2026-08-15 15:30 – Updated: 2026-08-17 06:33
VLAI
Details

In the Linux kernel, the following vulnerability has been resolved:

um: vector: fix use-after-free in vector_mmsg_rx()

When vector_mmsg_rx() discards a packet whose overlay header fails verify_header(), it frees the skb and continues the loop:

if (header_check < 0) {
    dev_kfree_skb_irq(skb);
    vp->estats.rx_encaps_errors++;
    continue;
}

The normal and short-packet paths fall through to the bottom of the loop body, which clears the consumed slot and advances the cursors:

(*skbuff_vector) = NULL;
mmsg_vector++;
skbuff_vector++;

The verify_header() < 0 path skips that via continue, so the freed skb is left in skbuff_vector[] and the cursors do not advance. The next iteration reads the same slot, gets the freed skb, and frees it again, producing a refcount underflow / use-after-free in the RX path.

Discard the slot the same way the other paths do before continuing.

Only transports whose verify_header() can return negative are affected: GRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not), so any peer on such a transport can trigger it without authentication.

Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Show details on source website
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{
  "affected": [],
  "aliases": [
    "CVE-2026-74478"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-15T13:17:52Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\num: vector: fix use-after-free in vector_mmsg_rx()\n\nWhen vector_mmsg_rx() discards a packet whose overlay header fails\nverify_header(), it frees the skb and continues the loop:\n\n\tif (header_check \u003c 0) {\n\t\tdev_kfree_skb_irq(skb);\n\t\tvp-\u003eestats.rx_encaps_errors++;\n\t\tcontinue;\n\t}\n\nThe normal and short-packet paths fall through to the bottom of the\nloop body, which clears the consumed slot and advances the cursors:\n\n\t(*skbuff_vector) = NULL;\n\tmmsg_vector++;\n\tskbuff_vector++;\n\nThe verify_header() \u003c 0 path skips that via continue, so the freed skb\nis left in skbuff_vector[] and the cursors do not advance. The next\niteration reads the same slot, gets the freed skb, and frees it again,\nproducing a refcount underflow / use-after-free in the RX path.\n\nDiscard the slot the same way the other paths do before continuing.\n\nOnly transports whose verify_header() can return negative are affected:\nGRE and L2TPv3 do so on a cookie/session-id mismatch (raw/tap do not),\nso any peer on such a transport can trigger it without authentication.",
  "id": "GHSA-mhmm-jqvj-99w7",
  "modified": "2026-08-17T06:33:48Z",
  "published": "2026-08-15T15:30:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-74478"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/180ff4c81faf01ec4e06082c9daa7c40518ead89"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4b9601595e8b6b5d18878cac0aeabc687d241111"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/67d58ab4f2ccf7145f3da07e025735a09c79de1b"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/804b681002ead233abf49a3efd681f5468a835f9"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/af421e9aed3920c7ac88c24daa48606c7112feca"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}



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