{"api_version":"1","generated_at":"2026-07-22T06:01:52+00:00","cve":"CVE-2026-63920","urls":{"html":"https://cve.report/CVE-2026-63920","api":"https://cve.report/api/cve/CVE-2026-63920.json","docs":"https://cve.report/api","cve_org":"https://www.cve.org/CVERecord?id=CVE-2026-63920","nvd":"https://nvd.nist.gov/vuln/detail/CVE-2026-63920"},"summary":{"title":"ipv6: validate extension header length before copying to cmsg","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: validate extension header length before copying to cmsg\n\nip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR}\ncmsgs (and their IPV6_2292* legacy counterparts) by trusting the\non-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length.\nThe length was validated only at parse time (ipv6_parse_hopopts(),\netc.).  An nftables payload-write expression can rewrite hdrlen after\nparsing and before the skb reaches recvmsg; the write itself is\nin-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040\nbytes from an 8-byte header.  nftables is reachable from an\nunprivileged user namespace, so this is an unprivileged\nslab-out-of-bounds read:\n\n  BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540\n   put_cmsg+0x3ac/0x540\n   udpv6_recvmsg+0xca0/0x1250\n   sock_recvmsg+0xdf/0x190\n   ____sys_recvmsg+0x1b1/0x620\n\nAdd ipv6_get_exthdr_len() which validates that at least two bytes\nare accessible before reading the hdrlen field, then checks the\ncomputed length against skb_tail_pointer(skb), returning 0 on\nfailure.  Extension headers are kept in the linear skb area by\npskb_may_pull() during input, so skb_tail_pointer() is the correct\nbound.\n\nUse ipv6_get_exthdr_len() at all non-AH call sites: the five\nstandalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR)\nand the three standard cases in the extension-header walk loop\n(DSTOPTS, ROUTING, default).  AH retains an inline bounds check\nbecause its length formula differs ((ptr[1]+2)<<2).\n\nThe walk loop also gets a pre-read bounds check at the top to\nvalidate ptr before any case accesses ptr[0] or ptr[1].\n\nWhen the walk loop detects a corrupted header, return from the\nfunction instead of continuing to process later socket options.","state":"PUBLISHED","assigner":"Linux","published_at":"2026-07-19 16:17:10","updated_at":"2026-07-20 15:16:56"},"problem_types":[],"metrics":[{"version":"3.1","source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","score":"7.1","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","data":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","baseScore":7.1,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"NONE","availabilityImpact":"HIGH"}},{"version":"3.1","source":"CNA","type":"DECLARED","score":"7.1","severity":"HIGH","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","data":{"baseScore":7.1,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","version":"3.1"}}],"references":[{"url":"https://git.kernel.org/stable/c/81394827dfb72772c50d0ae3bdfa094428a5d76d","name":"https://git.kernel.org/stable/c/81394827dfb72772c50d0ae3bdfa094428a5d76d","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/a35daeabb433686234b010ebf7b53778dbd6c9b8","name":"https://git.kernel.org/stable/c/a35daeabb433686234b010ebf7b53778dbd6c9b8","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/08464413e628803bd10cb1df68d0138665f2f885","name":"https://git.kernel.org/stable/c/08464413e628803bd10cb1df68d0138665f2f885","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/eb18a1b1644e4cad978df2131e2bb9a2e6886992","name":"https://git.kernel.org/stable/c/eb18a1b1644e4cad978df2131e2bb9a2e6886992","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/931b4a1f13408c2507719890f78f7227c34a0282","name":"https://git.kernel.org/stable/c/931b4a1f13408c2507719890f78f7227c34a0282","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/dd433671fef381fdaf7b530c631e6b782d66e224","name":"https://git.kernel.org/stable/c/dd433671fef381fdaf7b530c631e6b782d66e224","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/a29768d56eb3798c052ad3281b05596e695a17af","name":"https://git.kernel.org/stable/c/a29768d56eb3798c052ad3281b05596e695a17af","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://git.kernel.org/stable/c/0d330eff318c0f44d4fb0ad2c2aef38f87f24c90","name":"https://git.kernel.org/stable/c/0d330eff318c0f44d4fb0ad2c2aef38f87f24c90","refsource":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","tags":[],"title":"","mime":"","httpstatus":"","archivestatus":"0"},{"url":"https://www.cve.org/CVERecord?id=CVE-2026-63920","name":"CVE Program record","refsource":"CVE.ORG","tags":["canonical"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-63920","name":"NVD vulnerability detail","refsource":"NVD","tags":["canonical","analysis"]}],"affected":[{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 81394827dfb72772c50d0ae3bdfa094428a5d76d git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 931b4a1f13408c2507719890f78f7227c34a0282 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 08464413e628803bd10cb1df68d0138665f2f885 git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 a29768d56eb3798c052ad3281b05596e695a17af git","platforms":[]},{"source":"CNA","vendor":"Linux","product":"Linux","version":"affected 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original_commit_for_fix","platforms":[]}],"timeline":[],"solutions":[],"workarounds":[],"exploits":[],"credits":[],"nvd_cpes":[],"vendor_comments":[],"enrichments":{"kev":null,"epss":{"cve_year":"2026","cve_id":"63920","cve":"CVE-2026-63920","epss":"0.002100000","percentile":"0.113610000","score_date":"2026-07-20","updated_at":"2026-07-21 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the Linux kernel, the following vulnerability has been resolved:\n\nipv6: validate extension header length before copying to cmsg\n\nip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR}\ncmsgs (and their IPV6_2292* legacy counterparts) by trusting the\non-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length.\nThe length was validated only at parse time (ipv6_parse_hopopts(),\netc.).  An nftables payload-write expression can rewrite hdrlen after\nparsing and before the skb reaches recvmsg; the write itself is\nin-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040\nbytes from an 8-byte header.  nftables is reachable from an\nunprivileged user namespace, so this is an unprivileged\nslab-out-of-bounds read:\n\n  BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540\n   put_cmsg+0x3ac/0x540\n   udpv6_recvmsg+0xca0/0x1250\n   sock_recvmsg+0xdf/0x190\n   ____sys_recvmsg+0x1b1/0x620\n\nAdd ipv6_get_exthdr_len() which validates that at least two bytes\nare accessible before reading the hdrlen field, then checks the\ncomputed length against skb_tail_pointer(skb), returning 0 on\nfailure.  Extension headers are kept in the linear skb area by\npskb_may_pull() during input, so skb_tail_pointer() is the correct\nbound.\n\nUse ipv6_get_exthdr_len() at all non-AH call sites: the five\nstandalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR)\nand the three standard cases in the extension-header walk loop\n(DSTOPTS, ROUTING, default).  AH retains an inline bounds check\nbecause its length formula differs ((ptr[1]+2)<<2).\n\nThe walk loop also gets a pre-read bounds check at the top to\nvalidate ptr before any case accesses ptr[0] or ptr[1].\n\nWhen the walk loop detects a corrupted header, return from the\nfunction instead of continuing to process later socket options."}],"metrics":[{"cvssV3_1":{"baseScore":7.1,"baseSeverity":"HIGH","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","version":"3.1"}}],"providerMetadata":{"dateUpdated":"2026-07-20T13:41:30.071Z","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","shortName":"Linux"},"references":[{"url":"https://git.kernel.org/stable/c/81394827dfb72772c50d0ae3bdfa094428a5d76d"},{"url":"https://git.kernel.org/stable/c/931b4a1f13408c2507719890f78f7227c34a0282"},{"url":"https://git.kernel.org/stable/c/08464413e628803bd10cb1df68d0138665f2f885"},{"url":"https://git.kernel.org/stable/c/a29768d56eb3798c052ad3281b05596e695a17af"},{"url":"https://git.kernel.org/stable/c/0d330eff318c0f44d4fb0ad2c2aef38f87f24c90"},{"url":"https://git.kernel.org/stable/c/a35daeabb433686234b010ebf7b53778dbd6c9b8"},{"url":"https://git.kernel.org/stable/c/eb18a1b1644e4cad978df2131e2bb9a2e6886992"},{"url":"https://git.kernel.org/stable/c/dd433671fef381fdaf7b530c631e6b782d66e224"}],"title":"ipv6: validate extension header length before copying to cmsg","x_generator":{"engine":"bippy-1.2.0"}}},"cveMetadata":{"assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","assignerShortName":"Linux","cveId":"CVE-2026-63920","datePublished":"2026-07-19T14:55:22.813Z","dateReserved":"2026-07-19T07:54:57.020Z","dateUpdated":"2026-07-20T13:41:30.071Z","state":"PUBLISHED"},"dataType":"CVE_RECORD","dataVersion":"5.2"},"nvd":{"publishedDate":"2026-07-19 16:17:10","lastModifiedDate":"2026-07-20 15:16:56","problem_types":[],"metrics":{"cvssMetricV31":[{"source":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","type":"Secondary","cvssData":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H","baseScore":7.1,"baseSeverity":"HIGH","attackVector":"LOCAL","attackComplexity":"LOW","privilegesRequired":"LOW","userInteraction":"NONE","scope":"UNCHANGED","confidentialityImpact":"HIGH","integrityImpact":"NONE","availabilityImpact":"HIGH"},"exploitabilityScore":1.8,"impactScore":5.2}]},"configurations":[]},"legacy_mitre":{"record":{"CveYear":"2026","CveId":"63920","Ordinal":"1","Title":"ipv6: validate extension header length before copying to cmsg","CVE":"CVE-2026-63920","Year":"2026"},"notes":[{"CveYear":"2026","CveId":"63920","Ordinal":"1","NoteData":"In the Linux kernel, the following vulnerability has been resolved:\n\nipv6: validate extension header length before copying to cmsg\n\nip6_datagram_recv_specific_ctl() builds IPV6_{HOPOPTS,DSTOPTS,RTHDR}\ncmsgs (and their IPV6_2292* legacy counterparts) by trusting the\non-wire hdrlen byte (ptr[1]) when computing the put_cmsg() length.\nThe length was validated only at parse time (ipv6_parse_hopopts(),\netc.).  An nftables payload-write expression can rewrite hdrlen after\nparsing and before the skb reaches recvmsg; the write itself is\nin-bounds but put_cmsg() then reads up to ((hdrlen+1) << 3) = 2040\nbytes from an 8-byte header.  nftables is reachable from an\nunprivileged user namespace, so this is an unprivileged\nslab-out-of-bounds read:\n\n  BUG: KASAN: slab-out-of-bounds in put_cmsg+0x3ac/0x540\n   put_cmsg+0x3ac/0x540\n   udpv6_recvmsg+0xca0/0x1250\n   sock_recvmsg+0xdf/0x190\n   ____sys_recvmsg+0x1b1/0x620\n\nAdd ipv6_get_exthdr_len() which validates that at least two bytes\nare accessible before reading the hdrlen field, then checks the\ncomputed length against skb_tail_pointer(skb), returning 0 on\nfailure.  Extension headers are kept in the linear skb area by\npskb_may_pull() during input, so skb_tail_pointer() is the correct\nbound.\n\nUse ipv6_get_exthdr_len() at all non-AH call sites: the five\nstandalone cmsg blocks (HbH, 2292HbH, 2292DSTOPTS x2, 2292RTHDR)\nand the three standard cases in the extension-header walk loop\n(DSTOPTS, ROUTING, default).  AH retains an inline bounds check\nbecause its length formula differs ((ptr[1]+2)<<2).\n\nThe walk loop also gets a pre-read bounds check at the top to\nvalidate ptr before any case accesses ptr[0] or ptr[1].\n\nWhen the walk loop detects a corrupted header, return from the\nfunction instead of continuing to process later socket options.","Type":"Description","Title":"ipv6: validate extension header length before copying to cmsg"}]}}}