{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-63920", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.020Z", "datePublished": "2026-07-19T14:55:22.813Z", "dateUpdated": "2026-08-05T12:37:14.814Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:37:14.814Z" }, "descriptions": [ { "lang": "en", "value": "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." } ], "metrics": [ { "cvssV3_1": { "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" }, "scenarios": [ { "lang": "en", "value": "AV:L - Exploitation requires local syscalls (nftables netlink to install a payload-set rule, setsockopt for IPV6_RECV* options, and recvmsg). Although the trigger packet is received over IPv6, the mandatory nftables corruption step is classified as Local per kernel guidance.\nAC:L - The attacker fully controls the nftables payload-set rule, the on-wire extension header, socket receive options, and the recvmsg call, making the slab out-of-bounds read reliably reproducible without races or external conditions.\nPR:L - An unprivileged local user can create a user+network namespace, obtain CAP_NET_ADMIN there, configure nftables, open a UDPv6/raw socket with extension-header cmsg options, and trigger the bug without real root in the initial namespace.\nUI:N - No victim interaction is required; the attacker can send the crafted IPv6 datagram and call recvmsg on their own socket to trigger the out-of-bounds read.\nS:U - Impact is confined to kernel memory disclosure and potential kernel instability within the same kernel security domain; it does not cross a VM/host or IOMMU boundary.\nC:H - put_cmsg() can copy up to 2040 bytes past the actual extension header into userspace ancillary data, leaking adjacent slab/kernel memory (confirmed by KASAN slab-out-of-bounds in put_cmsg).\nI:N - The bug is an out-of-bounds read that copies kernel data to userspace; it does not modify kernel memory, corrupt control structures, or provide a write primitive.\nA:H - The out-of-bounds slab read can provoke a KASAN fault/kernel oops during put_cmsg(), and repeated triggering can deny availability of the affected system." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ipv6/datagram.c" ], "versions": [ { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "81394827dfb72772c50d0ae3bdfa094428a5d76d", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "931b4a1f13408c2507719890f78f7227c34a0282", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "08464413e628803bd10cb1df68d0138665f2f885", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "a29768d56eb3798c052ad3281b05596e695a17af", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "0d330eff318c0f44d4fb0ad2c2aef38f87f24c90", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "a35daeabb433686234b010ebf7b53778dbd6c9b8", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "eb18a1b1644e4cad978df2131e2bb9a2e6886992", "status": "affected", "versionType": "git" }, { "version": "1da177e4c3f41524e886b7f1b8a0c1fc7321cac2", "lessThan": "dd433671fef381fdaf7b530c631e6b782d66e224", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/ipv6/datagram.c" ], "versions": [ { "version": "2.6.12", "status": "affected" }, { "version": "0", "lessThan": "2.6.12", "status": "unaffected", "versionType": "semver" }, { "version": "5.10.259", "lessThanOrEqual": "5.10.*", "status": "unaffected", "versionType": "semver" }, { "version": "5.15.210", "lessThanOrEqual": "5.15.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.1.176", "lessThanOrEqual": "6.1.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.6.143", "lessThanOrEqual": "6.6.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.93", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.35", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.0.12", "lessThanOrEqual": "7.0.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.1", "lessThanOrEqual": "*", "status": "unaffected", "versionType": "original_commit_for_fix" } ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "5.10.259" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "5.15.210" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.1.176" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.6.143" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.12.93" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "6.18.35" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "7.0.12" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.12", "versionEndExcluding": "7.1" } ] } ] } ], "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" } } } }