CVE-2026-63829 (GCVE-0-2026-63829)
Vulnerability from cvelistv5
Published
2026-07-19 12:02
Modified
2026-08-17 04:51
Severity ?
8.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink A tunnel changelink() operates on at most two netns, dev_net(dev) and the tunnel link netns t->net. They differ once the device is created in or moved to a netns other than the one the request runs in. The rtnl changelink path checks CAP_NET_ADMIN only against dev_net(dev), so a caller privileged there but not in t->net can rewrite a tunnel that lives in t->net. Add rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in net/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is skipped when the link netns is dev_net(dev), where the rtnl path already checked it. The other patches in this series use the same helper. Gate ipgre_changelink() and erspan_changelink() with it, at the top of the op before any attribute is parsed, because the parsers update live tunnel fields first. ipgre_netlink_parms() sets t->collect_md before ip_tunnel_changelink() runs. Commit 8b484efd5cb4 ("ip6: vti: Use ip6_tnl.net in vti6_siocdevprivate().") added the same check on the ioctl path. This adds it on RTM_NEWLINK.
References
Impacted products
Vendor Product Version
Linux Linux Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
Version: b57708add31494175be741ed3fd24023b50c3423
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "include/net/rtnetlink.h",
            "net/core/rtnetlink.c",
            "net/ipv4/ip_gre.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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            "net/core/rtnetlink.c",
            "net/ipv4/ip_gre.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "3.16"
            },
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              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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              "version": "5.10.261",
              "versionType": "semver"
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              "status": "unaffected",
              "version": "5.15.212",
              "versionType": "semver"
            },
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              "status": "unaffected",
              "version": "6.1.178",
              "versionType": "semver"
            },
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              "version": "6.6.145",
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            },
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              "status": "unaffected",
              "version": "6.12.95",
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            },
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              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.38",
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              "status": "unaffected",
              "version": "7.1.3",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
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                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "5.10.261",
                  "versionStartIncluding": "3.16",
                  "vulnerable": true
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                  "vulnerable": true
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                  "vulnerable": true
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                {
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                  "versionEndExcluding": "7.2",
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                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ip_gre: require CAP_NET_ADMIN in the device netns for changelink\n\nA tunnel changelink() operates on at most two netns, dev_net(dev) and\nthe tunnel link netns t-\u003enet. They differ once the device is created in\nor moved to a netns other than the one the request runs in. The rtnl\nchangelink path checks CAP_NET_ADMIN only against dev_net(dev), so a\ncaller privileged there but not in t-\u003enet can rewrite a tunnel that\nlives in t-\u003enet.\n\nAdd rtnl_dev_link_net_capable() next to rtnl_get_net_ns_capable() in\nnet/core/rtnetlink.c. It requires CAP_NET_ADMIN in the link netns and is\nskipped when the link netns is dev_net(dev), where the rtnl path already\nchecked it. The other patches in this series use the same helper.\n\nGate ipgre_changelink() and erspan_changelink() with it, at the top of\nthe op before any attribute is parsed, because the parsers update live\ntunnel fields first. ipgre_netlink_parms() sets t-\u003ecollect_md before\nip_tunnel_changelink() runs.\n\nCommit 8b484efd5cb4 (\"ip6: vti: Use ip6_tnl.net in\nvti6_siocdevprivate().\") added the same check on the ioctl path. This\nadds it on RTM_NEWLINK."
        }
      ],
      "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 - Exploitation requires sending RTM_NEWLINK changelink requests over rtnetlink (netlink socket), matching the kernel guidance that tc/netlink configuration paths are Local.\nAC:L - Once a cross-namespace GRE/ERSPAN device is present in the caller\u0027s netns, triggering the bug is a single deterministic netlink changelink with no races or attacker-uncontrollable timing.\nPR:L - The rtnl entry path requires CAP_NET_ADMIN in dev_net(dev), which an unprivileged user can obtain inside a user namespace via unshare --user --map-root-user --net without real init-namespace root.\nUI:N - Exploitation is fully programmatic through netlink; no victim user action such as opening a file or mounting a filesystem is required.\nS:C - The changelink mutates tunnel state in t-\u003enet while authorization is checked only against dev_net(dev), crossing from the attacker\u0027s net/user namespace into another tenant\u0027s or the host\u0027s network namespace tunnel tables.\nC:H - An attacker can rewrite IFLA_GRE_REMOTE/LOCAL, keys, and related tunnel parameters to redirect GRE/ERSPAN traffic through attacker-controlled endpoints and read tunneled payloads.\nI:H - Unauthorized changelink updates live tunnel fields (including collect_md and encap parameters parsed before the missing check), enabling arbitrary redirection or injection of traffic in the victim link netns.\nA:H - Rewriting tunnel endpoints, keys, or metadata handling can break production GRE/ERSPAN overlays and VPN paths, causing sustained loss of connectivity for dependent services."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T04:51:37.933Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/19275943d8fe903eb7b9aa53e380e41efd042ada"
        },
        {
          "url": "https://git.kernel.org/stable/c/866b0f5ae599490bd496fd84581c68ac8b94e6af"
        },
        {
          "url": "https://git.kernel.org/stable/c/92b766fc55156e0da2ecd0c2302c971118f8a229"
        },
        {
          "url": "https://git.kernel.org/stable/c/e54c05ed3d9c28733fb9e5837219aca3691defa3"
        },
        {
          "url": "https://git.kernel.org/stable/c/9831bc9ecb402957810c2045c663fbfe9b09e296"
        },
        {
          "url": "https://git.kernel.org/stable/c/1697957eb0971d420dde42862b88eb43506a1105"
        },
        {
          "url": "https://git.kernel.org/stable/c/47b5d3d506609b08b2e1f7c14f0b681a1953d572"
        },
        {
          "url": "https://git.kernel.org/stable/c/8165f7ff57d9667d2bb477ef6af83ede7fed4ad7"
        }
      ],
      "title": "net: ip_gre: require CAP_NET_ADMIN in the device netns for changelink",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63829",
    "datePublished": "2026-07-19T12:02:23.191Z",
    "dateReserved": "2026-07-19T07:54:57.014Z",
    "dateUpdated": "2026-08-17T04:51:37.933Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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