CVE-2026-63968 (GCVE-0-2026-63968)

Vulnerability from cvelistv5 – Published: 2026-07-19 14:55 – Updated: 2026-08-05 12:37
VLAI
Title
ipv6: fix possible infinite loop in fib6_select_path()
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
Severity
7.5 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: d0ec61c9f3583b76aebdbb271f5c0d3fcccd48b2 , < 3948a7d92f7678e89e1776bb2d169afcad63b1ae (git)
Affected: 52da02521ede55fb86546c3fffd9377b3261b91f , < c87cd3cb309634bc8f50a54e2079424f219ac21f (git)
Affected: 34a949e7a0869dfa31a40416d2a56973fae1807b , < 0f7b73c3452635de83b8711b31abdda8e49aad7b (git)
Affected: d9ccb18f83ea2bb654289b6ecf014fd267cc988b , < ab9a10969a907b472a0196d999c08ff7144172e3 (git)
Affected: d9ccb18f83ea2bb654289b6ecf014fd267cc988b , < 9b9d5bd6e3d4c9cecab5407604b690684b2532d2 (git)
Affected: d9ccb18f83ea2bb654289b6ecf014fd267cc988b , < 9c7da87c2dc860bb17ca1ece942495d28b1ce3b9 (git)
Affected: 11edcd026012ac18acee0f1514db3ed1b160fc6f (git)
Affected: 6.1.128 , < 6.1.176 (semver)
Affected: 6.6.75 , < 6.6.143 (semver)
Affected: 6.12.2 , < 6.12.93 (semver)
Affected: 6.11.11 , < 6.12 (semver)
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Linux Linux Affected: 6.13
Unaffected: 0 , < 6.13 (semver)
Unaffected: 6.1.176 , ≤ 6.1.* (semver)
Unaffected: 6.6.143 , ≤ 6.6.* (semver)
Unaffected: 6.12.93 , ≤ 6.12.* (semver)
Unaffected: 6.18.35 , ≤ 6.18.* (semver)
Unaffected: 7.0.12 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
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          "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"
        }
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              "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."
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            "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"
          }
        ],
        "id": "CVE-2026-63968",
        "lastModified": "2026-07-30T14:51:11.223",
        "metrics": {
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                "confidentialityImpact": "NONE",
                "integrityImpact": "NONE",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
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        "vulnStatus": "Awaiting Analysis"
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      "current_release_date": "2026-07-22T07:05:47+00:00",
      "cve": "CVE-2026-63968",
      "id": "CVE-2026-63968",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_affected": "198",
      "product_status:known_not_affected": "76",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ipv6: fix possible infinite loop in fib6_select_path()",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63968.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-09-10T16:48:52Z",
      "cve": "CVE-2026-63968",
      "id": "CVE-2026-63968",
      "initial_release_date": "2026-07-21T13:02:32Z",
      "product_status:first_fixed": "2",
      "product_status:known_affected": "423",
      "product_status:known_not_affected": "251",
      "product_status:recommended": "281",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-63968",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-63968.json",
      "version": "18"
    }
  }
}



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  • 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.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.


Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.