{"id":"CVE-2026-63984","url":"https://www.cyber-defence.io/tools/cve/CVE-2026-63984","generatedAt":"2026-10-28T00:28:30.582Z","title":"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.","description":"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->hdrlen = (((n + 1) * sizeof(struct in6_addr)) >> 3);\n\nhdrlen is __u8. For n >= 127 the result exceeds 255 and silently\ntruncates. With n=127 (cmpri=15, cmpre=15, pad=0, hdrlen=16):\n\n    (128 * 16) >> 3 = 256, truncated to 0 as __u8\n\nThe caller in ipv6_rpl_srh_rcv() then places the compressed header\nat buf + ((ohdr->hdrlen + 1) << 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) > 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 <= 255, yet hdrlen=256 does not\nfit.\n\nTighten the bound to (n + 1) > 127. This caps n at 126, giving\nhdrlen = (127 * 16) >> 3 = 254, which fits in __u8. The compressed\nheader then lands at buf + ((254 + 1) << 3) = buf + 2040, exactly\npast the decompressed region (buf[0..2039]). No overlap. 127\nsegments is well beyond any realistic RPL deployment.","published":"2026-07-19T16:17:18.000Z","lastModified":"2026-10-19T21:17:16.000Z","status":"Undergoing Analysis","sourceIdentifier":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","cvss":{"version":"3.1","score":9.8,"severity":"CRITICAL","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"},"cwe":["CWE-190"],"affected":[],"epss":{"score":0.00514,"percentile":0.43541,"date":"2026-10-26","history":[]},"kev":{"listed":false},"exploits":{"count":0,"verified":false,"firstPublished":null,"source":"Exploit-DB (https://gitlab.com/exploit-database/exploitdb)","entries":[]},"verdict":{"level":"high","text":"High impact if exploited, but EPSS currently rates exploitation as unlikely (0.51%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit."},"changes":[],"references":[{"url":"https://git.kernel.org/stable/c/3618b34942b76471d044369bfd30d58c39068bf1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/6fe1cb312038516cb4d9fa089d700af7059f1a64","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/75b3680047bf09af8e7e471a7a6ddf2ce5847f56","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/97e06791368c01f0ad2a4b3269c2abe19485ca32","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/9d5e7a46a9f6d8f503b41bfefef70659845f1679","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/c0487a9c1e116cf349e2d1f302d9019670460858","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/de02fc049352af5a9595f015511222d0a85c326b","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"},{"url":"https://git.kernel.org/stable/c/fd238c51b0fa5390cceca9f1ac5a9ffda8063eed","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67"}],"sources":{"nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63984","epss":"https://www.first.org/epss/","kev":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog","exploitdb":"https://www.exploit-db.com/"},"licence":"CC BY 4.0 — link back to the CVE Explorer if you publish the results; upstream data remains subject to its own terms."}