CVE-2026-74727 (GCVE-0-2026-74727)

Vulnerability from cvelistv5 – Published: 2026-08-22 15:33 – Updated: 2026-08-25 05:42
VLAI
Title
ovpn: skip rehash for peers already removed from by_id
Summary
In the Linux kernel, the following vulnerability has been resolved: ovpn: skip rehash for peers already removed from by_id ovpn_nl_peer_set_doit() resolves the target peer via ovpn_peer_get_by_id() before taking ovpn->lock. In the window between the lookup (which only takes a refcount) and the subsequent spin_lock_bh(&ovpn->lock), a concurrent OVPN_CMD_PEER_DEL, keepalive expiry, or socket teardown can take ovpn->lock first, run ovpn_peer_remove() to unhash the peer from all four tables (by_id, by_vpn_addr4/6, by_transp_addr) and release the lock. set_doit then acquires ovpn->lock and calls ovpn_peer_hash_vpn_ip(), which re-inserts the now-removed peer back into the rehashing tables. The same race affects the float path: ovpn_peer_endpoints_update() holds only a refcount and acquires ovpn->lock very late (after async AEAD decrypt and a netlink notification), then rehashes the peer in the by_transp_addr table. The resurrected peer becomes reachable again from the RX lookup (ovpn_peer_get_by_transp_addr) and the TX VPN-IP lookup, even though userspace believes it is gone. Once the data-path refcount drops the peer is freed via call_rcu while the hash entries embedded in it remain linked, opening a UAF window. Bail out of the rehash when hash_entry_id is unhashed, mirroring the sentinel already used by ovpn_peer_remove() to detect the already-removed state. The check is safe under ovpn->lock, which serializes every mutation of hash_entry_id, and is a no-op for the add path because ovpn_peer_add_mp() inserts hash_entry_id before calling ovpn_peer_hash_vpn_ip().
Severity
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6666 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 1d36a36f6d5347360ef9681a05f6166683bafd1d , < d20c181088984b6eaa8d7fe7cb5ab3510988df59 (git)
Affected: 1d36a36f6d5347360ef9681a05f6166683bafd1d , < 66745480298775f188b2f5ad266643e85a90f73b (git)
Affected: 1d36a36f6d5347360ef9681a05f6166683bafd1d , < 33ec10567fe14456063daf549fdf1a4f53448e4c (git)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.18.45 , ≤ 6.18.* (semver)
Unaffected: 7.1.9 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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          "programFiles": [
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              "versionType": "semver"
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              "status": "unaffected",
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              "versionType": "original_commit_for_fix"
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                  "versionEndExcluding": "6.18.45",
                  "versionStartIncluding": "6.16",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.9",
                  "versionStartIncluding": "6.16",
                  "vulnerable": true
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              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novpn: skip rehash for peers already removed from by_id\n\novpn_nl_peer_set_doit() resolves the target peer via\novpn_peer_get_by_id() before taking ovpn-\u003elock. In the window between\nthe lookup (which only takes a refcount) and the subsequent\nspin_lock_bh(\u0026ovpn-\u003elock), a concurrent OVPN_CMD_PEER_DEL, keepalive\nexpiry, or socket teardown can take ovpn-\u003elock first, run\novpn_peer_remove() to unhash the peer from all four tables (by_id,\nby_vpn_addr4/6, by_transp_addr) and release the lock. set_doit then\nacquires ovpn-\u003elock and calls ovpn_peer_hash_vpn_ip(), which\nre-inserts the now-removed peer back into the rehashing tables.\n\nThe same race affects the float path: ovpn_peer_endpoints_update()\nholds only a refcount and acquires ovpn-\u003elock very late (after async\nAEAD decrypt and a netlink notification), then rehashes the peer\nin the by_transp_addr table.\n\nThe resurrected peer becomes reachable again from the RX lookup\n(ovpn_peer_get_by_transp_addr) and the TX VPN-IP lookup, even though\nuserspace believes it is gone. Once the data-path refcount drops the\npeer is freed via call_rcu while the hash entries embedded in it\nremain linked, opening a UAF window.\n\nBail out of the rehash when hash_entry_id is unhashed, mirroring\nthe sentinel already used by ovpn_peer_remove() to detect the\nalready-removed state. The check is safe under ovpn-\u003elock, which\nserializes every mutation of hash_entry_id, and is a no-op for the\nadd path because ovpn_peer_add_mp() inserts hash_entry_id before\ncalling ovpn_peer_hash_vpn_ip()."
        }
      ],
      "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 float-path UAF is reached from ovpn_udp_encap_recv()/ovpn_tcp_rcv() through ovpn_recv(), async AEAD decrypt, and ovpn_peer_endpoints_update(); a remote peer sends authenticated DATA_V2 packets over UDP/TCP to an internet-facing MP-mode OpenVPN gateway.\nAC:L - The remote peer controls float timing (new transport source), packet rate, and concurrent removal via TCP disconnect, UDP socket teardown, or keepalive expiry; netlink PEER_SET vs PEER_DEL races are likewise attacker-synchronized with no luck-dependent layout.\nPR:N - On an internet-facing MP-mode gateway, exploitation needs no Linux credentials on the victim\u2014only an established kernel-installed peer with valid AEAD keys (or namespace CAP_NET_ADMIN for netlink races), matching a remote VPN client rather than host root.\nUI:N - The rehash race is triggered by normal peer traffic and automatic keepalive/socket teardown; no administrator or end-user action on the victim host is required beyond routine VPN server operation.\nS:U - The UAF corrupts ovpn peer hash tables inside the kernel VPN driver; impact remains within the host kernel security domain without crossing VM, container, or IOMMU boundaries.\nC:H - Freed ovpn_peer objects remain linked in by_transp_addr/by_vpn_addr hash tables, so RX/TX lookups dereference recycled kmalloc-1k structures and enable arbitrary kernel-memory reads via attacker-controlled heap reuse.\nI:H - Resurrected hash entries steer traffic to freed peers and subsequent RCU/kref teardown on stale objects provide typical slab-UAF write primitives (refcount, socket, crypto pointer updates) suitable for kernel code execution.\nA:H - Use-after-free on hot datapath peer lookups reliably causes kernel oops/panic or slab corruption on VPN gateways, and remote peers can repeat the race to sustain denial of service."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-25T05:42:08.380Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
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          "url": "https://git.kernel.org/stable/c/d20c181088984b6eaa8d7fe7cb5ab3510988df59"
        },
        {
          "url": "https://git.kernel.org/stable/c/66745480298775f188b2f5ad266643e85a90f73b"
        },
        {
          "url": "https://git.kernel.org/stable/c/33ec10567fe14456063daf549fdf1a4f53448e4c"
        }
      ],
      "title": "ovpn: skip rehash for peers already removed from by_id",
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    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-74727",
    "datePublished": "2026-08-22T15:33:17.773Z",
    "dateReserved": "2026-08-15T05:44:03.929Z",
    "dateUpdated": "2026-08-25T05:42:08.380Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
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      "date": "2026-10-16",
      "epss": "0.00649",
      "percentile": "0.50069"
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                "defaultStatus": "unaffected",
                "product": "Linux",
                "programFiles": [
                  "drivers/net/ovpn/peer.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
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                "defaultStatus": "affected",
                "product": "Linux",
                "programFiles": [
                  "drivers/net/ovpn/peer.c"
                ],
                "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
                "vendor": "Linux",
                "versions": [
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                    "version": "6.16"
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          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novpn: skip rehash for peers already removed from by_id\n\novpn_nl_peer_set_doit() resolves the target peer via\novpn_peer_get_by_id() before taking ovpn-\u003elock. In the window between\nthe lookup (which only takes a refcount) and the subsequent\nspin_lock_bh(\u0026ovpn-\u003elock), a concurrent OVPN_CMD_PEER_DEL, keepalive\nexpiry, or socket teardown can take ovpn-\u003elock first, run\novpn_peer_remove() to unhash the peer from all four tables (by_id,\nby_vpn_addr4/6, by_transp_addr) and release the lock. set_doit then\nacquires ovpn-\u003elock and calls ovpn_peer_hash_vpn_ip(), which\nre-inserts the now-removed peer back into the rehashing tables.\n\nThe same race affects the float path: ovpn_peer_endpoints_update()\nholds only a refcount and acquires ovpn-\u003elock very late (after async\nAEAD decrypt and a netlink notification), then rehashes the peer\nin the by_transp_addr table.\n\nThe resurrected peer becomes reachable again from the RX lookup\n(ovpn_peer_get_by_transp_addr) and the TX VPN-IP lookup, even though\nuserspace believes it is gone. Once the data-path refcount drops the\npeer is freed via call_rcu while the hash entries embedded in it\nremain linked, opening a UAF window.\n\nBail out of the rehash when hash_entry_id is unhashed, mirroring\nthe sentinel already used by ovpn_peer_remove() to detect the\nalready-removed state. The check is safe under ovpn-\u003elock, which\nserializes every mutation of hash_entry_id, and is a no-op for the\nadd path because ovpn_peer_add_mp() inserts hash_entry_id before\ncalling ovpn_peer_hash_vpn_ip()."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\novpn: omitir el rehash para pares ya eliminados de by_id\n\novpn_nl_peer_set_doit() resuelve el par objetivo a trav\u00e9s de ovpn_peer_get_by_id() antes de tomar ovpn -\u003e lock. En la ventana entre la b\u00fasqueda (que solo toma un refcount) y el subsiguiente spin_lock_bh(\u0026ovpn -\u003e lock), un OVPN_CMD_PEER_DEL concurrente, la expiraci\u00f3n de un keepalive o el cierre de un socket pueden tomar ovpn -\u003e lock primero, ejecutar ovpn_peer_remove() para deshashear el par de las cuatro tablas (by_id, by_vpn_addr4/6, by_transp_addr) y liberar el bloqueo. set_doit luego adquiere ovpn -\u003e lock y llama a ovpn_peer_hash_vpn_ip(), lo que reinserta el par ahora eliminado de nuevo en las tablas de rehashing.\n\nLa misma condici\u00f3n de carrera afecta la ruta flotante: ovpn_peer_endpoints_update() solo mantiene un refcount y adquiere ovpn -\u003e lock muy tarde (despu\u00e9s de un descifrado AEAD as\u00edncrono y una notificaci\u00f3n netlink), luego rehashea el par en la tabla by_transp_addr.\n\nEl par resucitado vuelve a ser accesible desde la b\u00fasqueda RX (ovpn_peer_get_by_transp_addr) y la b\u00fasqueda TX VPN-IP, aunque el userspace cree que ha desaparecido. Una vez que el refcount de la ruta de datos disminuye, el par es liberado a trav\u00e9s de call_rcu mientras que las entradas de hash incrustadas en \u00e9l permanecen vinculadas, abriendo una ventana UAF.\n\nSalir del rehash cuando hash_entry_id es deshasheado, reflejando el centinela ya utilizado por ovpn_peer_remove() para detectar el estado ya eliminado. La verificaci\u00f3n es segura bajo ovpn -\u003e lock, que serializa cada mutaci\u00f3n de hash_entry_id, y es una operaci\u00f3n nula para la ruta de adici\u00f3n porque ovpn_peer_add_mp() inserta hash_entry_id antes de llamar a ovpn_peer_hash_vpn_ip()."
          }
        ],
        "id": "CVE-2026-74727",
        "lastModified": "2026-10-14T13:10:00.187",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "HIGH",
                "baseScore": 9.8,
                "baseSeverity": "CRITICAL",
                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "NONE",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
                "version": "3.1"
              },
              "exploitabilityScore": 3.9,
              "impactScore": 5.9,
              "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
              "type": "Secondary"
            }
          ]
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        "published": "2026-08-22T16:16:47.813",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/33ec10567fe14456063daf549fdf1a4f53448e4c"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/66745480298775f188b2f5ad266643e85a90f73b"
          },
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/d20c181088984b6eaa8d7fe7cb5ab3510988df59"
          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Received"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-25T08:56:33+00:00",
      "cve": "CVE-2026-74727",
      "id": "CVE-2026-74727",
      "initial_release_date": "2026-08-22T00:00:00+00:00",
      "product_status:known_not_affected": "274",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ovpn: skip rehash for peers already removed from by_id",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74727.json",
      "version": "3"
    }
  }
}



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