IPv6 stable and temporary interface identifiers derived from a non-cryptographic PRNG secret key

{
  "id": "31566ecc2affd18a7f2c4c07014490869753cfd5f3cb0cf24ab2c2c990d224a1",
  "url": "https://www.cve.org/CVERecord?id=CVE-2026-19742",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "IPv6 stable and temporary interface identifiers derived from a non-cryptographic PRNG secret key",
    "summary": "The IPv6 stack derived the long-lived secret key used to compute RFC 7217 stable interface identifiers (gen_stable_iid() in subsys/net/ip/ipv6.c) and RFC 8981 temporary interface identifiers (gen_temporary_iid() in subsys/net/ip/ipv6_pe.c) with sys_rand_get(). That API is documented as not cryptographically secure, while both RFCs require this key to be an unpredictable random value of at least 128 bits — the unpredictability of every generated IID rests entirely on it. Depending on the platform, sys_rand_get() resolves either to a hardware entropy device or, on boards whose entropy driver sets CONFIG_ENTROPY_NEEDS_PRNG, to the non-cryptographic xoshiro128++ generator in subsys/random/random_xoshiro128.c, which keeps a single global 128-bit state shared with every other sys_rand_get() consumer. Many of those consumers put their output directly on the wire (ephemeral source ports, DNS query IDs, CoAP message IDs and tokens, DHCPv6 transaction IDs, WebSocket masking keys), and the xoshiro state transition is invertible, so an observer of a device's traffic can recover the generator state and reconstruct the IID secret key. Additionally, with the entropy-device backend sys_rand_get() silently falls back to k_cycle_get_32() samples when the entropy driver fails, and returns no error, so the key could be derived from the cycle counter without the caller noticing. With the key known, stable IIDs become directly computable for any prefix (the remaining HMAC inputs — prefix, interfac",
    "evidence": "cve:CVE-2026-19742",
    "products": [
      {
        "name": {
          "value": "zephyr",
          "evidence": "/containers/cna/affected/0/product"
        },
        "prerequisites": [],
        "fixed_versions": [],
        "affected_versions": []
      }
    ],
    "severity": "low",
    "structured": {
      "id": "CVE-2026-19742",
      "aliases": [
        "CVE-2026-19742"
      ],
      "metrics": [
        {
          "format": "CVSS",
          "cvssV3_1": {
            "version": "3.1",
            "baseScore": 3.7,
            "baseSeverity": "LOW",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N"
          }
        }
      ],
      "affected": [
        {
          "vendor": "zephyrproject",
          "product": "zephyr",
          "versions": [
            {
              "status": "affected",
              "version": "3.7.0",
              "lessThan": "4.5.0",
              "versionType": "semver"
            }
          ],
          "packageName": "zephyr",
          "programFiles": [
            "subsys/net/ip/ipv6.c",
            "subsys/net/ip/ipv6_pe.c"
          ],
          "collectionURL": "https://github.com/zephyrproject-rtos/zephyr",
          "defaultStatus": "unaffected",
          "programRoutines": [
            {
              "name": "gen_stable_iid"
            },
            {
              "name": "gen_temporary_iid"
            }
          ]
        }
      ],
      "modified": "2026-10-26T17:37:10.987Z",
      "provider": "cve",
      "references": [
        "https://github.com/zephyrproject-rtos/zephyr/commit/253315829d3cb5906c660d8418d8408d40bd266f",
        "https://github.com/zephyrproject-rtos/zephyr/security/advisories/GHSA-xfm2-gr93-8mx9"
      ],
      "provider_metadata": {
        "adp": [
          {
            "title": "CISA ADP Vulnrichment",
            "metrics": [
              {
                "other": {
                  "type": "ssvc",
                  "content": {
                    "id": "CVE-2026-19742",
                    "role": "CISA Coordinator",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "partial"
                      }
                    ],
                    "version": "2.0.3",
                    "timestamp": "2026-10-26T16:58:23.799989Z"
                  }
                }
              }
            ],
            "providerMetadata": {
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP",
              "dateUpdated": "2026-10-26T17:37:10.987Z"
            }
          }
        ],
        "cna": {
          "orgId": "e2e69745-5e70-4e92-8431-deb5529a81ad",
          "shortName": "zephyr",
          "dateUpdated": "2026-10-26T16:08:51.255Z"
        }
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-19742",
        "evidence": "/cveMetadata/cveId"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/containers/cna/metrics"
  },
  "source_id": "core-cve",
  "document_id": 326391,
  "published_at": "2026-10-26T16:08:51.255+00:00"
}