{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2"
            },
            {
              "fixed": "81394827dfb72772c50d0ae3bdfa094428a5d76d"
            },
            {
              "fixed": "931b4a1f13408c2507719890f78f7227c34a0282"
            },
            {
              "fixed": "08464413e628803bd10cb1df68d0138665f2f885"
            },
            {
              "fixed": "a29768d56eb3798c052ad3281b05596e695a17af"
            },
            {
              "fixed": "0d330eff318c0f44d4fb0ad2c2aef38f87f24c90"
            },
            {
              "fixed": "a35daeabb433686234b010ebf7b53778dbd6c9b8"
            },
            {
              "fixed": "eb18a1b1644e4cad978df2131e2bb9a2e6886992"
            },
            {
              "fixed": "dd433671fef381fdaf7b530c631e6b782d66e224"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.6.12"
            },
            {
              "fixed": "5.10.259"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.11.0"
            },
            {
              "fixed": "5.15.210"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.16.0"
            },
            {
              "fixed": "6.1.176"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.2.0"
            },
            {
              "fixed": "6.6.143"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.7.0"
            },
            {
              "fixed": "6.12.93"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.35"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "7.0.12"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63920.json"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: validate extension header length before copying to cmsg\n\nip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR}\ncmsgs (and their IPV6_2292* legacy counterparts) by trusting the\non-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length.\nThe length was validated only at parse time (ipv6_parse_hopopts(),\netc.).  An nftables payload-write expression can rewrite hdrlen after\nparsing and before the skb reaches recvmsg; the write itself is\nin-bounds but put_cmsg() then reads up to ((hdrlen+1) \u003c\u003c 3) = 2040\nbytes from an 8-byte header.  nftables is reachable from an\nunprivileged user namespace, so this is an unprivileged\nslab-out-of-bounds read:\n\n  BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540\n   put_cmsg+0x3ac/0x540\n   udpv6_recvmsg+0xca0/0x1250\n   sock_recvmsg+0xdf/0x190\n   ____sys_recvmsg+0x1b1/0x620\n\nAdd ipv6_get_exthdr_len() which validates that at least two bytes\nare accessible before reading the hdrlen field, then checks the\ncomputed length against skb_tail_pointer(skb), returning 0 on\nfailure.  Extension headers are kept in the linear skb area by\npskb_may_pull() during input, so skb_tail_pointer() is the correct\nbound.\n\nUse ipv6_get_exthdr_len() at all non-AH call sites: the five\nstandalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR)\nand the three standard cases in the extension-header walk loop\n(DSTOPTS, ROUTING, default).  AH retains an inline bounds check\nbecause its length formula differs ((ptr[1]+2)\u003c\u003c2).\n\nThe walk loop also gets a pre-read bounds check at the top to\nvalidate ptr before any case accesses ptr[0] or ptr[1].\n\nWhen the walk loop detects a corrupted header, return from the\nfunction instead of continuing to process later socket options.",
  "id": "CVE-2026-63920",
  "modified": "2026-07-22T05:29:49.402097789Z",
  "published": "2026-07-19T14:55:22.813Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/08464413e628803bd10cb1df68d0138665f2f885"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/0d330eff318c0f44d4fb0ad2c2aef38f87f24c90"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/81394827dfb72772c50d0ae3bdfa094428a5d76d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/931b4a1f13408c2507719890f78f7227c34a0282"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a29768d56eb3798c052ad3281b05596e695a17af"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a35daeabb433686234b010ebf7b53778dbd6c9b8"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/dd433671fef381fdaf7b530c631e6b782d66e224"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/eb18a1b1644e4cad978df2131e2bb9a2e6886992"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63920.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63920"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.8.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "ipv6: validate extension header length before copying to cmsg"
}