CVE-2026-63984 (GCVE-0-2026-63984)
Vulnerability from cvelistv5
Published
2026-07-19 14:56
Modified
2026-10-19 20:18
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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          "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."
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    "datePublished": "2026-07-19T14:56:06.786Z",
    "dateReserved": "2026-07-19T07:54:57.025Z",
    "dateUpdated": "2026-10-19T20:18:00.765Z",
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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.\"}]}], \"affected\": [{\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"75b3680047bf09af8e7e471a7a6ddf2ce5847f56\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"fd238c51b0fa5390cceca9f1ac5a9ffda8063eed\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"3618b34942b76471d044369bfd30d58c39068bf1\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"97e06791368c01f0ad2a4b3269c2abe19485ca32\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"de02fc049352af5a9595f015511222d0a85c326b\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"6fe1cb312038516cb4d9fa089d700af7059f1a64\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"c0487a9c1e116cf349e2d1f302d9019670460858\", \"versionType\": \"git\"}, {\"status\": \"affected\", \"version\": \"8610c7c6e3bd647ff98d21c8bc0580e77bc2f8b3\", \"lessThan\": \"9d5e7a46a9f6d8f503b41bfefef70659845f1679\", \"versionType\": \"git\"}], \"programFiles\": [\"net/ipv6/exthdrs.c\"], \"defaultStatus\": \"unaffected\"}, {\"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\", \"vendor\": \"Linux\", \"product\": \"Linux\", \"versions\": [{\"status\": \"affected\", \"version\": \"5.7\"}, {\"status\": \"unaffected\", \"version\": \"0\", \"lessThan\": \"5.7\", \"versionType\": \"semver\"}, {\"status\": \"unaffected\", \"version\": \"5.10.259\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.10.*\"}, {\"status\": \"unaffected\", \"version\": \"5.15.210\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"5.15.*\"}, {\"status\": \"unaffected\", \"version\": \"6.1.176\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.1.*\"}, {\"status\": \"unaffected\", \"version\": \"6.6.143\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.6.*\"}, {\"status\": \"unaffected\", \"version\": \"6.12.93\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.12.*\"}, {\"status\": \"unaffected\", \"version\": \"6.18.35\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"6.18.*\"}, {\"status\": \"unaffected\", \"version\": \"7.0.12\", \"versionType\": \"semver\", \"lessThanOrEqual\": \"7.0.*\"}, {\"status\": \"unaffected\", \"version\": \"7.1\", \"versionType\": \"original_commit_for_fix\", \"lessThanOrEqual\": \"*\"}], \"programFiles\": [\"net/ipv6/exthdrs.c\"], \"defaultStatus\": \"affected\"}], \"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\"}], \"x_generator\": {\"engine\": \"bippy-1.2.0\"}, \"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.\"}], \"cpeApplicability\": [{\"nodes\": [{\"negate\": false, \"cpeMatch\": [{\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.10.259\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"5.15.210\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.1.176\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.6.143\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.12.93\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"6.18.35\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.0.12\", \"versionStartIncluding\": \"5.7\"}, {\"criteria\": \"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\", \"vulnerable\": true, \"versionEndExcluding\": \"7.1\", \"versionStartIncluding\": \"5.7\"}], \"operator\": \"OR\"}]}], \"providerMetadata\": {\"orgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"shortName\": \"Linux\", \"dateUpdated\": \"2026-08-05T12:37:52.442Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-63984\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-19T20:18:00.765Z\", \"dateReserved\": \"2026-07-19T07:54:57.025Z\", \"assignerOrgId\": \"416baaa9-dc9f-4396-8d5f-8c081fb06d67\", \"datePublished\": \"2026-07-19T14:56:06.786Z\", \"assignerShortName\": \"Linux\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


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