123 lines
9.4 KiB
JSON
123 lines
9.4 KiB
JSON
{
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"dataType": "CVE_RECORD",
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"dataVersion": "5.2",
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"cveMetadata": {
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"cveId": "CVE-2026-98869",
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"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"state": "PUBLISHED",
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"assignerShortName": "Linux",
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"dateReserved": "2026-09-25T10:25:14.377Z",
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"datePublished": "2026-10-21T14:55:10.364Z",
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"dateUpdated": "2026-10-24T14:09:25.680Z"
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},
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"containers": {
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"cna": {
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"providerMetadata": {
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"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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"shortName": "Linux",
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"dateUpdated": "2026-10-24T14:09:25.680Z"
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},
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"descriptions": [
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{
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"lang": "en",
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Infer zext_dst based on static register liveness analysis\n\nAs reported in the thread [1], the verifier's 32-bit operations zero\nextension logic is broken. This logic is responsible for correct\nsemantics of 32-bit operations on s390 architecture.\n\nAccording to BPF semantics, operation `w1 += 1` is supposed to zero\nextend the upper half of the register `r1`. On s390 the JIT relies on\nthe verifier emitting explicit zero extension before such operations.\n\nThe verifier attempts to minimize the amount of zero extensions\ninserted by tracking whether upper halves of the 64-bit registers are\never used. Previously such tracking worked as follows:\n\n- bpf_reg_state->subreg_def field was set by do_check_insn()\n for each operation defining lower but not the upper halves\n of the register.\n- Whenever an operation reading the whole register was verified,\n the verifier checked register's subreg_def and set\n bpf_insn_aux_data->zext_dst flag as true via a call to\n mark_insn_zext() function.\n- After the verification was complete, a special pass\n bpf_opt_subreg_zext_lo32_rnd_hi32() extended 32-bit operations\n with bpf_insn_aux_data->zext_dst set as true by adding\n explicit zero extension.\n\nNote that the logic above relies on bpf_reg_state->subreg_def,\nwhich is a property of a current verifier state.\nBefore the commit [2] two additional steps happened:\n\n- The verifier tracked upper and lower register halves' liveness as\n flags REG_LIVE_READ{32,64} in bpf_reg_state->live.\n- The function propagate_liveness() called mark_insn_zext()\n in order to transfer the knowledge about which registers have\n their upper halves alive (and thus might require zero extension).\n\nThe commit [2] removed the two steps described above,\nhence making possible a situation like below:\n\n- The register's upper half is set and is used on some verification\n path P1 and the register happens not to be marked as precise.\n- The checkpoint C is created while processing some instruction\n between register initialization and usage.\n- On some other verification path P2 the register's upper half is not\n initialized and that path ends hitting the checkpoint C.\n- In such a case the register's initialization on path P2 would lack\n zext_dst mark, making it possible for the program to inject\n an arbitrary value in the register's upper half.\n\nThis commit replaces subreg_def based logic with computing zext_dst\nstatically, as a part of the bpf_compute_live_registers() analysis:\n\n- The analysis now tracks usage of upper and lower halves of the\n registers separately.\n- If some instruction defines a 32-bit subregister, but not the whole\n register, *and* the upper half of the register is alive after that\n instruction, the instruction is marked as zext_dst.\n\nThere is one notable drop in precision: whenever a BPF subprogram is\ncalled, all 64 bits of parameter registers are presumed to be used.\nThe assumption is that such a drop in precision would not inflict\na noticeable performance penalty.\n\n[1] https://lore.kernel.org/bpf/CAGKGUv=sOuqQtA1Ub-5JXfA4FPosJFYKAQE4B79cK+P1erxqtg@mail.gmail.com/\n[2] commit 107e16979905 (\"bpf: disable and remove registers chain based liveness\")"
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}
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],
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"metrics": [
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{
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"cvssV3_1": {
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"version": "3.1",
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"vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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"baseScore": 7.8,
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"baseSeverity": "HIGH"
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},
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"scenarios": [
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{
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"lang": "en",
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"value": "AV:L - Crafted bytecode enters through bpf(BPF_PROG_LOAD) → bpf_prog_load() → bpf_check() → patched bpf_compute_live_registers(); no network protocol supplies it, and the socket filter is locally loaded and attached.\nAC:L - bpf_is_state_visited() checkpoints attacker-supplied control flow, letting one path fully define R6 and a pruned path execute W6=32 before a 64-bit use; the attacker controls both paths and the retained high bits, with no race or external timing.\nPR:L - bpf_prog_load() permits BPF_PROG_TYPE_SOCKET_FILTER without CAP_BPF when sysctl_unprivileged_bpf_disabled is 0; exploitation was reproduced as uid 1000 with empty capability sets, and BPF tokens separately support namespaced CAP_BPF delegation.\nUI:N - The attacker loads the program, attaches it to an owned socket through SO_ATTACH_BPF, and supplies traffic to execute it; no action by another user is required.\nS:U - The bpf verifier and s390 JIT fault, ARRAY-map out-of-bounds accesses, and resulting current-process credential modification all remain within the host kernel's security authority; no VM or IOMMU boundary is crossed.\nC:H - The missing zext_dst lets attacker-controlled upper bits form an unchecked 64-bit offset from an ARRAY map-value pointer; the demonstrated exploit disclosed map->ops, derived the KASLR slide, and obtained arbitrary kernel reads.\nI:H - The same unchecked ARRAY map-value offset provides arbitrary kernel writes; the demonstrated exploit located and modified the calling process's credentials to obtain uid 0.\nA:H - The arbitrary kernel-write primitive created by the omitted s390 zero-extension can corrupt kernel objects or control-flow data, causing an oops or system crash in addition to privilege escalation."
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}
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]
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}
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],
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"affected": [
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "unaffected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"include/linux/bpf_verifier.h",
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"kernel/bpf/fixups.c",
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"kernel/bpf/liveness.c",
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"kernel/bpf/verifier.c"
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],
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"versions": [
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{
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"version": "107e169799057bc6a379ddb625cbe1e51cfc7d72",
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"lessThan": "7ce090afbf725e25fff29caacce1eaf8459b1117",
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"status": "affected",
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"versionType": "git"
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}
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]
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},
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{
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"product": "Linux",
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"vendor": "Linux",
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"defaultStatus": "affected",
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"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
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"programFiles": [
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"include/linux/bpf_verifier.h",
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"kernel/bpf/fixups.c",
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"kernel/bpf/liveness.c",
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"kernel/bpf/verifier.c"
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],
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"versions": [
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{
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"version": "6.18",
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"status": "affected"
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},
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{
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"version": "0",
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"lessThan": "6.18",
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"status": "unaffected",
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"versionType": "semver"
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},
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{
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"version": "7.3",
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"lessThanOrEqual": "*",
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"status": "unaffected",
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"versionType": "original_commit_for_fix"
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}
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]
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}
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],
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"cpeApplicability": [
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{
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"nodes": [
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{
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"operator": "OR",
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"negate": false,
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"cpeMatch": [
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{
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"vulnerable": true,
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"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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"versionStartIncluding": "6.18",
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"versionEndExcluding": "7.3"
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}
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]
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}
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]
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}
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],
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"references": [
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{
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"url": "https://git.kernel.org/stable/c/7ce090afbf725e25fff29caacce1eaf8459b1117"
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}
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],
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"title": "bpf: Infer zext_dst based on static register liveness analysis",
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"x_generator": {
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"engine": "bippy-1.2.0"
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}
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