CVE-2026-74561 (GCVE-0-2026-74561)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:28 – Updated: 2026-08-17 05:48
VLAI
Title
nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush
Summary
In the Linux kernel, the following vulnerability has been resolved: nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush nh_rt_cache_flush() walks nh->f6i_list during an RTNL-serialized nexthop replace without holding nh->lock, racing the unlocked IPv6 route add/delete that mutate the list under nh->lock and free fib6_info entries (nh_rt_cache_flush() is inlined into rtm_new_nexthop()): BUG: KASAN: slab-use-after-free in nh_rt_cache_flush (net/ipv4/nexthop.c:2243) Read of size 8 at addr ffff888012953e18 by task exploit/146 nh_rt_cache_flush (net/ipv4/nexthop.c:2243) replace_nexthop (net/ipv4/nexthop.c:2610) rtm_new_nexthop (net/ipv4/nexthop.c:3323) rtnetlink_rcv_msg (net/core/rtnetlink.c:7076) Unlike the other f6i_list walks, this one bumps each route's sernum via fib6_update_sernum_upto_root(), which needs tb6_lock; taking nh->lock around it would invert the established tb6_lock -> nh->lock order and deadlock. As the only purpose is to invalidate cached dsts, bump the IPv6 sernum for the whole netns with rt_genid_bump_ipv6() instead, mirroring the rt_cache_flush() already done for IPv4 just above.
Severity
8.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 081efd18326e353c6fbfdeff903a83edde953f72 , < 44f53e4331a30fabc38a411fae7524341b618db3 (git)
Affected: 081efd18326e353c6fbfdeff903a83edde953f72 , < 4787a6d2629b4e8c0b6bacab1f75c1660eca44d9 (git)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv4/nexthop.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "versionType": "git"
            },
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.16",
                  "vulnerable": true
                },
                {
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              "operator": "OR"
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      "descriptions": [
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush\n\nnh_rt_cache_flush() walks nh-\u003ef6i_list during an RTNL-serialized nexthop\nreplace without holding nh-\u003elock, racing the unlocked IPv6 route\nadd/delete that mutate the list under nh-\u003elock and free fib6_info\nentries (nh_rt_cache_flush() is inlined into rtm_new_nexthop()):\n\n  BUG: KASAN: slab-use-after-free in nh_rt_cache_flush (net/ipv4/nexthop.c:2243)\n  Read of size 8 at addr ffff888012953e18 by task exploit/146\n   nh_rt_cache_flush (net/ipv4/nexthop.c:2243)\n   replace_nexthop (net/ipv4/nexthop.c:2610)\n   rtm_new_nexthop (net/ipv4/nexthop.c:3323)\n   rtnetlink_rcv_msg (net/core/rtnetlink.c:7076)\n\nUnlike the other f6i_list walks, this one bumps each route\u0027s sernum via\nfib6_update_sernum_upto_root(), which needs tb6_lock; taking nh-\u003elock\naround it would invert the established tb6_lock -\u003e nh-\u003elock order and\ndeadlock. As the only purpose is to invalidate cached dsts, bump the\nIPv6 sernum for the whole netns with rt_genid_bump_ipv6() instead,\nmirroring the rt_cache_flush() already done for IPv4 just above."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 8.8,
            "baseSeverity": "HIGH",
            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:L - The slab use-after-free is reached only via local RTNETLINK on AF_NETLINK sockets: RTM_NEWNEXTHOP with NLM_F_REPLACE drives replace_nexthop()-\u003enh_rt_cache_flush(), racing concurrent RTM_NEWROUTE/RTM_DELROUTE IPv6 route changes; it is not triggered by remote packet processing.\nAC:L - The race is attacker-controlled: one thread replaces a nexthop under rtnl_net_lock while another concurrently adds/deletes IPv6 routes via unlocked inet6_rtm_newroute/inet6_rtm_delroute handlers; Microsoft reproduced reliable KASAN slab-use-after-free with this pattern.\nPR:L - rtnetlink_rcv_msg() requires CAP_NET_ADMIN via netlink_net_capable() for all non-GET handlers; unprivileged local users obtain this inside a user/network namespace (unshare -Urn), not only init-namespace root.\nUI:N - No victim interaction is required; exploitation is fully attacker-driven through coordinated local netlink nexthop replace and IPv6 route add/delete commands from attacker-controlled processes.\nS:C - A successful UAF from CAP_NET_ADMIN inside an unprivileged user/network namespace corrupts host kernel slab memory and can escape the namespace/container sandbox to compromise the host system, crossing the container-to-host security boundary.\nC:H - The unlocked nh-\u003ef6i_list walk dereferences freed fib6_info objects (KASAN read of size 8 at nh_rt_cache_flush), enabling arbitrary kernel memory disclosure via slab heap reuse of attacker-groomed objects.\nI:H - Beyond the UAF read, fib6_update_sernum_upto_root() writes fn_sernum through stale fib6_info/fib6_table pointers; slab UAF on fib6_info provides memory corruption primitives for arbitrary kernel writes and local privilege escalation.\nA:H - The confirmed KASAN slab-use-after-free in nh_rt_cache_flush during nexthop replace causes kernel oops/panic; UAF list walks are inherently crash-prone and can be triggered repeatedly for denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:48:40.842Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/44f53e4331a30fabc38a411fae7524341b618db3"
        },
        {
          "url": "https://git.kernel.org/stable/c/4787a6d2629b4e8c0b6bacab1f75c1660eca44d9"
        }
      ],
      "title": "nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush",
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        "engine": "bippy-1.2.0"
      }
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74561",
    "datePublished": "2026-08-15T12:28:04.525Z",
    "dateReserved": "2026-08-15T05:44:03.916Z",
    "dateUpdated": "2026-08-17T05:48:40.842Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-74561",
      "date": "2026-08-18",
      "epss": "0.00112",
      "percentile": "0.01592"
    },
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    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-17T15:01:01+00:00",
      "cve": "CVE-2026-74561",
      "id": "CVE-2026-74561",
      "initial_release_date": "2026-08-15T00:00:00+00:00",
      "product_status:known_affected": "76",
      "product_status:known_not_affected": "198",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: nexthop: avoid unlocked f6i_list walk in nh_rt_cache_flush",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74561.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-17T16:25:08Z",
      "cve": "CVE-2026-74561",
      "id": "CVE-2026-74561",
      "initial_release_date": "2026-08-15T23:50:11Z",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-74561",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-74561.json",
      "version": "3"
    }
  }
}



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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.
  • 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.


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