CVE-2026-63968 (GCVE-0-2026-63968)
Vulnerability from cvelistv5
Published
2026-07-19 14:55
Modified
2026-08-05 12:37
Severity ?
7.5 (High) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: fix possible infinite loop in fib6_select_path() Found while auditing the same pattern Sashiko reported in rt6_fill_node() [1]. Apply the same fix as commit f8d8ce1b515a ("ipv6: fix possible infinite loop in fib6_info_uses_dev()"). Writers holding tb6_lock can list_del_rcu(&first->fib6_siblings) without waiting for RCU readers; first->fib6_siblings.next then still points into the old ring and this softirq-side walker never reaches &first->fib6_siblings as its terminator. fib6_purge_rt() always WRITE_ONCE()s first->fib6_nsiblings to 0 before list_del_rcu(), so an inside-loop check is a reliable detach signal. [1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev
References
Impacted products
Vendor Product Version
Linux Linux Version: d0ec61c9f3583b76aebdbb271f5c0d3fcccd48b2
Version: 52da02521ede55fb86546c3fffd9377b3261b91f
Version: 34a949e7a0869dfa31a40416d2a56973fae1807b
Version: d9ccb18f83ea2bb654289b6ecf014fd267cc988b
Version: d9ccb18f83ea2bb654289b6ecf014fd267cc988b
Version: d9ccb18f83ea2bb654289b6ecf014fd267cc988b
Version: 11edcd026012ac18acee0f1514db3ed1b160fc6f
Version: 6.1.128   ≤
Version: 6.6.75   ≤
Version: 6.12.2   ≤
Version: 6.11.11   ≤
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{
  "containers": {
    "cna": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/route.c"
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          "vendor": "Linux",
          "versions": [
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              "version": "0",
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              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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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 possible infinite loop in fib6_select_path()\n\nFound while auditing the same pattern Sashiko reported in\nrt6_fill_node() [1]. Apply the same fix as\ncommit f8d8ce1b515a (\"ipv6: fix possible infinite loop in fib6_info_uses_dev()\").\n\nWriters holding tb6_lock can list_del_rcu(\u0026first-\u003efib6_siblings)\nwithout waiting for RCU readers; first-\u003efib6_siblings.next then\nstill points into the old ring and this softirq-side walker never\nreaches \u0026first-\u003efib6_siblings as its terminator. fib6_purge_rt()\nalways WRITE_ONCE()s first-\u003efib6_nsiblings to 0 before\nlist_del_rcu(), so an inside-loop check is a reliable detach signal.\n\n[1] https://sashiko.dev/#/patchset/20260526020227.4857-1-jiayuan.chen%40linux.dev"
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The vulnerable function is reached from the IPv6 packet receive path (ipv6_rcv \u2192 ip6_route_input \u2192 ip6_pol_route \u2192 fib6_select_path) in softirq context, and production lockups were observed during processing of incoming IPv6 traffic on internet-facing edge routers.\nAC:L - The race is reliably triggerable when an attacker influences both packet flow and route churn (e.g., user-namespace ECMP setup plus traffic, or remote traffic coinciding with BGP nexthop updates); a dedicated selftest reproduces soft lockups in under a minute under controlled conditions.\nPR:N - Triggering fib6_select_path() during packet processing requires only the ability to send IPv6 traffic to destinations using multipath routes; concurrent route-table updates can occur from infrastructure (BGP/dynamic routing) without the attacker holding any local privileges.\nUI:N - Exploitation requires no victim interaction beyond normal network traffic delivery to a host or router processing IPv6 packets.\nS:U - The impact is kernel CPU soft lockup and watchdog panic within the same kernel security boundary; there is no sandbox, VM, or IOMMU boundary crossing.\nC:N - The bug is an infinite loop over stale sibling-list pointers during RCU read-side traversal; it does not read or disclose attacker-controlled memory or kernel secrets.\nI:N - No data modification or memory corruption occurs; the failure mode is CPU hang from unbounded list iteration, not arbitrary write or code execution.\nA:H - The infinite loop in softirq context causes CPU soft lockup, and documented production and test cases show this leads to watchdog-triggered kernel panic, a complete loss of system availability."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:37:40.633Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/3948a7d92f7678e89e1776bb2d169afcad63b1ae"
        },
        {
          "url": "https://git.kernel.org/stable/c/c87cd3cb309634bc8f50a54e2079424f219ac21f"
        },
        {
          "url": "https://git.kernel.org/stable/c/0f7b73c3452635de83b8711b31abdda8e49aad7b"
        },
        {
          "url": "https://git.kernel.org/stable/c/ab9a10969a907b472a0196d999c08ff7144172e3"
        },
        {
          "url": "https://git.kernel.org/stable/c/9b9d5bd6e3d4c9cecab5407604b690684b2532d2"
        },
        {
          "url": "https://git.kernel.org/stable/c/9c7da87c2dc860bb17ca1ece942495d28b1ce3b9"
        }
      ],
      "title": "ipv6: fix possible infinite loop in fib6_select_path()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63968",
    "datePublished": "2026-07-19T14:55:55.620Z",
    "dateReserved": "2026-07-19T07:54:57.024Z",
    "dateUpdated": "2026-08-05T12:37:40.633Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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