{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-64009", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-07-19T07:54:57.026Z", "datePublished": "2026-07-19T14:56:24.448Z", "dateUpdated": "2026-08-05T12:38:09.114Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-08-05T12:38:09.114Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nxfrm: Check for underflow in xfrm_state_mtu\n\nLeo Lin reported OOB write issue in esp component:\n\n xfrm_state_mtu() returns u32 but performs its arithmetic in unsigned\n modulo-2^32 space using an attacker-influenced \"header_len + authsize +\n net_adj\" subtracted from a small \"mtu\" argument. A nobody user can\n install an IPv4 ESP tunnel SA with a large authentication key\n (XFRMA_ALG_AUTH_TRUNC, e.g. hmac(sha512), 64-byte key, 64-byte trunc),\n configure a small interface MTU (68 bytes), and set XFRMA_TFCPAD to a\n large value. When a single UDP datagram is then sent through the\n tunnel, xfrm_state_mtu() underflows to a near-2^32 value, and\n esp_output() consumes it as a signed int via:\n\n padto = min(x->tfcpad, xfrm_state_mtu(x, mtu_cached))\n esp.tfclen = padto - skb->len (assigned to int)\n\n esp.tfclen ends up negative (e.g. -207). It is sign-extended to size_t\n when passed to memset() inside esp_output_fill_trailer(), producing a\n ~16 EB write of zeroes at skb_tail_pointer(skb). KASAN logs it as\n \"Write of size 18446744073709551537 at addr ffff888...\".\n\nCheck for underflow and return 1. This causes the sendmsg attempt to\nfail with ENETUNREACH." } ], "metrics": [ { "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH" }, "scenarios": [ { "lang": "en", "value": "AV:L - The vulnerability is triggered on the local ESP output path when a process sends a UDP datagram through an attacker-configured XFRM tunnel via sendmsg(); remote peers cannot install XFRM SAs, set interface MTU, or control XFRMA_TFCPAD on the victim system.\nAC:L - The attacker fully controls all preconditions (ESP tunnel SA with large HMAC-SHA512 auth, MTU 68, XFRMA_TFCPAD, and UDP payload size) and can trigger the underflow deterministically with a single datagram as demonstrated in the fix commit.\nPR:L - XFRM state/policy installation and interface MTU configuration require CAP_NET_ADMIN, which an unprivileged local user can obtain in a user namespace via unshare -Urn; this is the most severe reasonable deployment scenario on multi-tenant hosts.\nUI:N - Exploitation requires only the attacker's own netlink configuration and socket send operations; no action from another user or administrator is needed.\nS:U - The vulnerability corrupts kernel heap memory from a local attacker's security context, constituting standard kernel privilege escalation rather than crossing a VM or hypervisor boundary.\nC:H - The bug produces a massive out-of-bounds write via memset() at the skb tail pointer; such heap corruption is exploitable for arbitrary kernel memory disclosure in addition to the demonstrated KASAN-detected write primitive.\nI:H - A negative tfclen sign-extended to size_t causes an enormous memset() OOB write at skb_tail_pointer(skb), providing a memory corruption primitive that can be leveraged for arbitrary kernel writes and code execution.\nA:H - The OOB write reliably triggers kernel oops/panic (KASAN reports a write of size 18446744073709551537 bytes), causing immediate system crash and denial of service." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "net/xfrm/xfrm_state.c" ], "versions": [ { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "8014f70c4e6e5ab101ae3860a614e65e988372e3", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "1021d2877b689a648b27815c854557a917122e93", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "2a41b1b31c61c52b972278ce1732a1443f5e89ed", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "fccd685b32df5aaf6bad4381eeda216468e283f0", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "820e501be8aee4b365d218d83227b314309c5fda", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "82ac903e0b519849647657b8c48d21237ada06a2", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "3db50ceeacb52806d8fe86fb1dfe944df0b9f789", "status": "affected", "versionType": "git" }, { "version": "c5c2523893747f88a83376abad310c8ad13f7197", "lessThan": "742b04d0550b0ec89dcbc99537ec88653bd1ad90", "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/xfrm/xfrm_state.c" ], "versions": [ { "version": "2.6.22", "status": "affected" }, { "version": "0", "lessThan": "2.6.22", "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": "2.6.22", "versionEndExcluding": "5.10.259" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "5.15.210" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "6.1.176" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "6.6.143" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "6.12.93" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "6.18.35" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "7.0.12" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "2.6.22", "versionEndExcluding": "7.1" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/8014f70c4e6e5ab101ae3860a614e65e988372e3" }, { "url": "https://git.kernel.org/stable/c/1021d2877b689a648b27815c854557a917122e93" }, { "url": "https://git.kernel.org/stable/c/2a41b1b31c61c52b972278ce1732a1443f5e89ed" }, { "url": "https://git.kernel.org/stable/c/fccd685b32df5aaf6bad4381eeda216468e283f0" }, { "url": "https://git.kernel.org/stable/c/820e501be8aee4b365d218d83227b314309c5fda" }, { "url": "https://git.kernel.org/stable/c/82ac903e0b519849647657b8c48d21237ada06a2" }, { "url": "https://git.kernel.org/stable/c/3db50ceeacb52806d8fe86fb1dfe944df0b9f789" }, { "url": "https://git.kernel.org/stable/c/742b04d0550b0ec89dcbc99537ec88653bd1ad90" } ], "title": "xfrm: Check for underflow in xfrm_state_mtu", "x_generator": { "engine": "bippy-1.2.0" } } } }