CVE-2026-68136 (GCVE-0-2026-68136)

Vulnerability from cvelistv5 – Published: 2026-08-10 11:58 – Updated: 2026-08-17 04:59
VLAI
Title
net: gro: fix double aggregation of flush-marked skbs
Summary
In the Linux kernel, the following vulnerability has been resolved: net: gro: fix double aggregation of flush-marked skbs Commit 0ab03f353d36 ("net-gro: Fix GRO flush when receiving a GSO packet.") added a flush check to skb_gro_receive(), but skb_gro_receive_list() lacks the same validation. As a result, packets marked with NAPI_GRO_CB(skb)->flush may still be re-aggregated. This allows already-GRO'd packets with existing frag_list to be re-aggregated into a new GRO session, corrupting the frag_list chain structure. When skb_segment() attempts to unpack these malformed packets, it encounters invalid state and triggers a kernel panic. Scenario (Tethering/Device forwarding): 1. Driver: Generated aggregated packet P1 via LRO with frag_list 2. Dev A: Receives aggregated fraglist packet and flush flag set 3. Dev A: Re-enters GRO, skb_gro_receive_list() is called 4. Missing flush check allows re-aggregation despite flush flag 5. Frag_list chain becomes corrupted (loops or dangling refs) 6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list Root cause in skb_segment(): The check at line ~4891: if (hsize <= 0 && i >= nfrags && skb_headlen(list_skb) && (skb_headlen(list_skb) == len || sg)) { When frag_list is corrupted by double aggregation, when list_skb is a NULL pointer from skb->next, skb_headlen(list_skb) dereference NULL/corrupted pointers occurs. Call Trace: skb_headlen(NULL skb) skb_segment tcp_gso_segment tcp4_gso_segment inet_gso_segment skb_mac_gso_segment __skb_gso_segment skb_gso_segment validate_xmit_skb validate_xmit_skb_list sch_direct_xmit qdisc_restart __qdisc_run qdisc_run net_tx_action Fix: Add NAPI_GRO_CB(skb)->flush validation to the early-return check in skb_gro_receive_list(), matching the defensive programming pattern of skb_gro_receive().
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 , < 107e1a469f53a2a70874f3f12bf6fcd23925da1d (git)
Affected: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 , < a4dfd46cc8f08a29c6183794790547d0945f3d45 (git)
Affected: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 , < fc0c0f7a207f0cd2d2aa725696c907f7d03af9e0 (git)
Affected: 3a1296a38d0cf62bffb9a03c585cbd5dbf15d596 , < e751256486d0ded20f5a9f9863467f1dce65142f (git)
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Linux Linux Affected: 5.6
Unaffected: 0 , < 5.6 (semver)
Unaffected: 6.12.101 , ≤ 6.12.* (semver)
Unaffected: 6.18.42 , ≤ 6.18.* (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "product": "Linux",
          "programFiles": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: gro: fix double aggregation of flush-marked skbs\n\nCommit 0ab03f353d36 (\"net-gro: Fix GRO flush when receiving a GSO\npacket.\") added a flush check to skb_gro_receive(), but\nskb_gro_receive_list() lacks the same validation.\n\nAs a result, packets marked with NAPI_GRO_CB(skb)-\u003eflush may still be\nre-aggregated.\n\nThis allows already-GRO\u0027d packets with existing frag_list to be\nre-aggregated into a new GRO session, corrupting the frag_list chain\nstructure. When skb_segment() attempts to unpack these malformed packets,\nit encounters invalid state and triggers a kernel panic.\n\nScenario (Tethering/Device forwarding):\n  1. Driver: Generated aggregated packet P1 via LRO with frag_list\n  2. Dev A: Receives aggregated fraglist packet and flush flag set\n  3. Dev A: Re-enters GRO, skb_gro_receive_list() is called\n  4. Missing flush check allows re-aggregation despite flush flag\n  5. Frag_list chain becomes corrupted (loops or dangling refs)\n  6. Dev B: TX path calls skb_segment(), crashes on corrupted frag_list\n\nRoot cause in skb_segment():\n  The check at line ~4891:\n    if (hsize \u003c= 0 \u0026\u0026 i \u003e= nfrags \u0026\u0026 skb_headlen(list_skb) \u0026\u0026\n        (skb_headlen(list_skb) == len || sg)) {\n\n  When frag_list is corrupted by double aggregation, when list_skb is\n  a NULL pointer from skb-\u003enext, skb_headlen(list_skb) dereference\n  NULL/corrupted pointers occurs.\n\nCall Trace:\n skb_headlen(NULL skb)\n skb_segment\n tcp_gso_segment\n tcp4_gso_segment\n inet_gso_segment\n skb_mac_gso_segment\n __skb_gso_segment\n skb_gso_segment\n validate_xmit_skb\n validate_xmit_skb_list\n sch_direct_xmit\n qdisc_restart\n __qdisc_run\n qdisc_run\n net_tx_action\n\nFix: Add NAPI_GRO_CB(skb)-\u003eflush validation to the early-return check in\nskb_gro_receive_list(), matching the defensive programming pattern of\nskb_gro_receive()."
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            "baseSeverity": "CRITICAL",
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              "value": "AV:N - The bug is reached from the standard NAPI GRO receive path processing remotely originated TCP/IP packets (napi_gro_receive\u2192dev_gro_receive\u2192tcp_gro_receive\u2192skb_gro_receive_list), including tethering/NAT/forwarding scenarios where packets re-enter GRO on a second netdev after driver LRO or prior GRO aggregation.\nAC:L - An attacker can reliably trigger the bug by crafting a TCP stream through a forwarding host with rx-gro-list enabled, without races or victim-specific timing; the commit documents a deterministic tethering/forwarding repro where flush-marked frag_list skbs are re-aggregated and later crash skb_segment.\nPR:N - No local privileges or authentication are required; any remote peer that can send TCP traffic through a vulnerable forwarding/tethering/NAT Linux host can reach the GRO fraglist merge path, which performs no capability or credential checks on the receive path.\nUI:N - Exploitation requires only network-delivered packets and normal kernel forwarding/GRO processing; the victim does not need to open files, mount filesystems, click links, or perform any deliberate action beyond routine network operation.\nS:U - Impact is confined to kernel memory corruption and panic within the same host kernel security domain during packet GRO aggregation and subsequent segmentation on transmit; it does not cross VM, container, or IOMMU boundaries to affect a separate security authority.\nC:H - Double aggregation corrupts the skb frag_list chain (loops, dangling references, NULL/corrupted list_skb pointers), constituting kernel heap memory corruption that can be read during skb_segment processing and is classifiable as a high-impact info-disclosure primitive beyond a simple crash.\nI:H - Re-aggregating flush-marked skbs with existing frag_list corrupts skb linked-list structure and reference relationships in kernel memory, enabling potential control of subsequent skb metadata and write/control-flow primitives during GSO segmentation, not merely integrity-preserving packet drops.\nA:H - Corrupted frag_list state causes skb_segment to dereference a NULL or invalid list_skb via skb_headlen(), producing a kernel panic/oops on the transmit path (sch_direct_xmit/qdisc_run), fully denying availability of the affected system."
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    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68136",
    "datePublished": "2026-08-10T11:58:59.450Z",
    "dateReserved": "2026-07-30T09:28:09.370Z",
    "dateUpdated": "2026-08-17T04:59:29.319Z",
    "state": "PUBLISHED"
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When skb_segment() attempts to unpack these malformed packets,\\nit encounters invalid state and triggers a kernel panic.\\n\\nScenario (Tethering/Device forwarding):\\n  1. Driver: Generated aggregated packet P1 via LRO with frag_list\\n  2. Dev A: Receives aggregated fraglist packet and flush flag set\\n  3. Dev A: Re-enters GRO, skb_gro_receive_list() is called\\n  4. Missing flush check allows re-aggregation despite flush flag\\n  5. Frag_list chain becomes corrupted (loops or dangling refs)\\n  6. 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    "redhat_vex": {
      "aggregate_severity": "Important",
      "current_release_date": "2026-08-18T02:59:11+00:00",
      "cve": "CVE-2026-68136",
      "id": "CVE-2026-68136",
      "initial_release_date": "2026-08-10T00:00:00+00:00",
      "product_status:known_affected": "232",
      "product_status:known_not_affected": "42",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: net: gro: fix double aggregation of flush-marked skbs",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68136.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-18T16:56:20Z",
      "cve": "CVE-2026-68136",
      "id": "CVE-2026-68136",
      "initial_release_date": "2026-08-18T16:56:20Z",
      "product_status:known_affected": "231",
      "product_status:known_not_affected": "65",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68136",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68136.json",
      "version": "2"
    }
  }
}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
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