CVE-2026-63984 (GCVE-0-2026-63984)
Vulnerability from cvelistv5
Published
2026-07-19 14:56
Modified
2026-08-05 12:37
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress() ipv6_rpl_srh_decompress() computes: outhdr->hdrlen = (((n + 1) * sizeof(struct in6_addr)) >> 3); hdrlen is __u8. For n >= 127 the result exceeds 255 and silently truncates. With n=127 (cmpri=15, cmpre=15, pad=0, hdrlen=16): (128 * 16) >> 3 = 256, truncated to 0 as __u8 The caller in ipv6_rpl_srh_rcv() then places the compressed header at buf + ((ohdr->hdrlen + 1) << 3). With hdrlen=0 this is buf + 8, but the decompressed region occupies buf[0..2055] (8-byte header plus 128 full addresses). The compressed header overlaps the decompressed data, and ipv6_rpl_srh_compress() writes into this overlap, corrupting the routing header of the forwarded packet. The existing guard at exthdrs.c:546 checks (n + 1) > 255, which prevents n+1 from overflowing unsigned char (the segments_left field), but does not prevent the computed hdrlen from overflowing __u8. n=127 passes because 128 <= 255, yet hdrlen=256 does not fit. Tighten the bound to (n + 1) > 127. This caps n at 126, giving hdrlen = (127 * 16) >> 3 = 254, which fits in __u8. The compressed header then lands at buf + ((254 + 1) << 3) = buf + 2040, exactly past the decompressed region (buf[0..2039]). No overlap. 127 segments is well beyond any realistic RPL deployment.
References
Impacted products
Vendor Product Version
Linux Linux Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
Version: 8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/ipv6/exthdrs.c"
          ],
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          "product": "Linux",
          "programFiles": [
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
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              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()\n\nipv6_rpl_srh_decompress() computes:\n\n    outhdr-\u003ehdrlen = (((n + 1) * sizeof(struct in6_addr)) \u003e\u003e 3);\n\nhdrlen is __u8. For n \u003e= 127 the result exceeds 255 and silently\ntruncates. With n=127 (cmpri=15, cmpre=15, pad=0, hdrlen=16):\n\n    (128 * 16) \u003e\u003e 3 = 256, truncated to 0 as __u8\n\nThe caller in ipv6_rpl_srh_rcv() then places the compressed header\nat buf + ((ohdr-\u003ehdrlen + 1) \u003c\u003c 3). With hdrlen=0 this is buf + 8,\nbut the decompressed region occupies buf[0..2055] (8-byte header\nplus 128 full addresses). The compressed header overlaps the\ndecompressed data, and ipv6_rpl_srh_compress() writes into this\noverlap, corrupting the routing header of the forwarded packet.\n\nThe existing guard at exthdrs.c:546 checks (n + 1) \u003e 255, which\nprevents n+1 from overflowing unsigned char (the segments_left\nfield), but does not prevent the computed hdrlen from overflowing\n__u8. n=127 passes because 128 \u003c= 255, yet hdrlen=256 does not\nfit.\n\nTighten the bound to (n + 1) \u003e 127. This caps n at 126, giving\nhdrlen = (127 * 16) \u003e\u003e 3 = 254, which fits in __u8. The compressed\nheader then lands at buf + ((254 + 1) \u003c\u003c 3) = buf + 2040, exactly\npast the decompressed region (buf[0..2039]). No overlap. 127\nsegments is well beyond any realistic RPL deployment."
        }
      ],
      "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 vulnerable code runs in the IPv6 routing-header receive handler on incoming packets; a remote attacker can deliver a crafted RFC 6554 type-3 RPL SRH to an RPL-enabled router or gateway over the network.\nAC:L - Triggering requires only a deterministically crafted SRH (e.g., n=127, CmprI=15, CmprE=15, pad=0, hdrlen=16, segments_left\u003e0); all of these fields are fully attacker-controlled once the target has rpl_seg_enabled.\nPR:N - No authentication or local privileges are needed to send the malicious IPv6 packet; rpl_seg_enabled is a victim-side deployment setting on RPL routers/gateways (IoT/industrial mesh), not an attacker privilege requirement.\nUI:N - Exploitation is achieved solely by sending a malformed network packet and does not require any action from a victim user.\nS:U - Impact is confined to kernel memory corruption and packet forwarding within the same kernel security boundary; this is not a VM escape, sandbox escape, or cross-authority boundary violation.\nC:H - The hdrlen truncation causes overlapping read/write of the same kmalloc buffer during decompress/recompress, constituting kernel heap memory corruption that can be leveraged for information disclosure primitives.\nI:H - ipv6_rpl_srh_compress() performs out-of-bounds writes into the overlapping decompressed region, corrupting routing-header data that is then memcpy\u0027d into the forwarded skb, enabling memory corruption exploitable for control-flow or data modification.\nA:H - Kernel heap corruption during SRH processing can cause kernel oops, panics, or repeated crashes when processing or forwarding the corrupted packet, consistent with high availability impact for memory-corruption bugs."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:37:52.442Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/75b3680047bf09af8e7e471a7a6ddf2ce5847f56"
        },
        {
          "url": "https://git.kernel.org/stable/c/fd238c51b0fa5390cceca9f1ac5a9ffda8063eed"
        },
        {
          "url": "https://git.kernel.org/stable/c/3618b34942b76471d044369bfd30d58c39068bf1"
        },
        {
          "url": "https://git.kernel.org/stable/c/97e06791368c01f0ad2a4b3269c2abe19485ca32"
        },
        {
          "url": "https://git.kernel.org/stable/c/de02fc049352af5a9595f015511222d0a85c326b"
        },
        {
          "url": "https://git.kernel.org/stable/c/6fe1cb312038516cb4d9fa089d700af7059f1a64"
        },
        {
          "url": "https://git.kernel.org/stable/c/c0487a9c1e116cf349e2d1f302d9019670460858"
        },
        {
          "url": "https://git.kernel.org/stable/c/9d5e7a46a9f6d8f503b41bfefef70659845f1679"
        }
      ],
      "title": "ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-63984",
    "datePublished": "2026-07-19T14:56:06.786Z",
    "dateReserved": "2026-07-19T07:54:57.025Z",
    "dateUpdated": "2026-08-05T12:37:52.442Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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