CVE-2026-72020 (GCVE-0-2026-72020)
Vulnerability from cvelistv5
Published
2026-08-15 05:51
Modified
2026-08-17 05:39
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ipvs: reset full ip_vs_seq structs in ip_vs_conn_new Commit 9a05475cebdd ("ipvs: avoid kmem_cache_zalloc in ip_vs_conn_new") changed ip_vs_conn_new() to allocate an ip_vs_conn object with kmem_cache_alloc(). The function then initializes many fields explicitly, but only resets in_seq.delta and out_seq.delta in the two struct ip_vs_seq members. That leaves init_seq and previous_delta uninitialized. This is normally harmless while the corresponding IP_VS_CONN_F_IN_SEQ or IP_VS_CONN_F_OUT_SEQ flag is clear. For connections learned from a sync message, however, ip_vs_proc_conn() preserves those flags from IP_VS_CONN_F_BACKUP_MASK and passes opt=NULL when the message omits IPVS_OPT_SEQ_DATA. In that case the new connection can be hashed with SEQ flags set but with the rest of in_seq/out_seq still containing stale slab data. When a packet for such a connection is later handled by an IPVS application helper, vs_fix_seq() and vs_fix_ack_seq() use previous_delta and init_seq to rewrite TCP sequence numbers. A malformed sync message can therefore make forwarded packets carry stale slab bytes in their TCP seq/ack numbers, and can also corrupt the forwarded TCP flow. Reset both struct ip_vs_seq members completely before publishing the connection. This matches the existing "reset struct ip_vs_seq" comment and keeps the sequence-adjustment gates inactive unless valid sequence data is installed later.
References
Impacted products
Vendor Product Version
Linux Linux Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
Version: 9a05475cebdd6341884b5901e53870be26e65158
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/netfilter/ipvs/ip_vs_conn.c"
          ],
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      "cpeApplicability": [
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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\nipvs: reset full ip_vs_seq structs in ip_vs_conn_new\n\nCommit 9a05475cebdd (\"ipvs: avoid kmem_cache_zalloc in\nip_vs_conn_new\") changed ip_vs_conn_new() to allocate an ip_vs_conn\nobject with kmem_cache_alloc().  The function then initializes many\nfields explicitly, but only resets in_seq.delta and out_seq.delta in the\ntwo struct ip_vs_seq members.\n\nThat leaves init_seq and previous_delta uninitialized.  This is normally\nharmless while the corresponding IP_VS_CONN_F_IN_SEQ or\nIP_VS_CONN_F_OUT_SEQ flag is clear.  For connections learned from a sync\nmessage, however, ip_vs_proc_conn() preserves those flags from\nIP_VS_CONN_F_BACKUP_MASK and passes opt=NULL when the message omits\nIPVS_OPT_SEQ_DATA.  In that case the new connection can be hashed with\nSEQ flags set but with the rest of in_seq/out_seq still containing stale\nslab data.\n\nWhen a packet for such a connection is later handled by an IPVS\napplication helper, vs_fix_seq() and vs_fix_ack_seq() use\nprevious_delta and init_seq to rewrite TCP sequence numbers.  A malformed\nsync message can therefore make forwarded packets carry stale slab bytes\nin their TCP seq/ack numbers, and can also corrupt the forwarded TCP\nflow.\n\nReset both struct ip_vs_seq members completely before publishing the\nconnection.  This matches the existing \"reset struct ip_vs_seq\" comment\nand keeps the sequence-adjustment gates inactive unless valid sequence\ndata is installed later."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is reached when a host running the IPVS backup sync receiver processes forged UDP sync datagrams (default multicast 224.0.0.81:8848) in ip_vs_process_message(), which is a network packet receive path rather than a local-only ioctl/netlink interface.\nAC:L - Once IPVS backup sync is enabled, an attacker can reliably send IPVS v1 messages that set IP_VS_CONN_F_IN_SEQ/OUT_SEQ while omitting IPVS_OPT_SEQ_DATA; no race, heap grooming, or victim-specific state beyond matching syncid (often 0) is required.\nPR:N - The backup sync socket accepts unauthenticated UDP input with no capability checks; only an optional syncid filter (frequently left at 0) may drop messages, so the attacker needs no Linux privileges to inject the malformed sync records.\nUI:N - No end-user or administrator interaction is required at exploit time; the attacker directly delivers crafted sync messages to the listening backup daemon without victims opening files, clicking links, or changing settings.\nS:U - Exploitation stays within the IPVS load balancer kernel/network authority and affects connections it forwards; it does not constitute a VM escape, sandbox breakout, or cross-security-authority boundary such as guest-to-host.\nC:H - Uninitialized ip_vs_seq init_seq and previous_delta fields retain stale slab data that vs_fix_seq()/vs_fix_ack_seq() apply when rewriting forwarded TCP seq/ack numbers, leaking kernel heap bytes onto the network to clients or backend servers.\nI:H - Those same uninitialized sequence-adjustment fields cause incorrect TCP sequence/ack rewriting in NAT/application-helper paths (ip_vs_app_pkt_in/out), corrupting load-balanced TCP flows and enabling attacker-driven manipulation of forwarded traffic integrity.\nA:H - Corrupted TCP sequence handling breaks or resets connections on the virtual service and can be triggered repeatedly via additional forged sync messages, causing sustained denial of service to load-balanced traffic on the affected backup node."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:39:30.496Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3bf9a260188b2a5449cbddc032a749ab433fe328"
        },
        {
          "url": "https://git.kernel.org/stable/c/6378c5cb360eb1750f88839d7c3613ea92ac1816"
        },
        {
          "url": "https://git.kernel.org/stable/c/32c299e28b8eea6cbbd23b97dc61401e9ef9c445"
        },
        {
          "url": "https://git.kernel.org/stable/c/9e36602cbec552286f7e691cfd366525c565ee74"
        },
        {
          "url": "https://git.kernel.org/stable/c/d0eed7177e822cab83141e5c44b2aa345c7fd379"
        },
        {
          "url": "https://git.kernel.org/stable/c/83fb4c2c5344f02eac929f66de3c9d1adfcde04c"
        },
        {
          "url": "https://git.kernel.org/stable/c/6335ab62d5fc9ed875279238233fba3462c168f5"
        },
        {
          "url": "https://git.kernel.org/stable/c/2975324d164c552b028632f107b567302863b7f6"
        }
      ],
      "title": "ipvs: reset full ip_vs_seq structs in ip_vs_conn_new",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-72020",
    "datePublished": "2026-08-15T05:51:46.675Z",
    "dateReserved": "2026-08-09T03:40:39.900Z",
    "dateUpdated": "2026-08-17T05:39:30.496Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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