{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-93127", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-17T16:02:15.087Z", "datePublished": "2026-09-17T16:11:31.253Z", "dateUpdated": "2026-10-19T09:06:00.545Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-19T09:06:00.545Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Drop scalar id on sign-extending narrowing stack fills\n\nWhen a spilled scalar is filled back with a sign-extending narrowing load\n(BPF_MEMSX), check_stack_read_fixed_off() copies the spilled register\nincluding its scalar id, but coerce_reg_to_size_sx() then sign-extends the\nfilled register's value. If the same slot is also filled with a plain\nzero-extending load (BPF_MEM), both destination registers share the id yet\nhold different values. A later 'if == const' then refines the\nsign-extended register through sync_linked_regs() to a value it does not\nhave at runtime (e.g. the verifier believes 0x80000000 while the register\nis 0xffffffff80000000), which can be turned into an out-of-bounds access.\n\nDrop the shared scalar id at the sign-extension site in check_mem_access()\nwhen sign extension actually changes the value, mirroring the BPF_MOVSX\nhandling in check_alu_op() (no_sext = reg_umax < 2^(size*8-1))." } ], "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 attacker-controlled input is BPF bytecode supplied via bpf(BPF_PROG_LOAD) in SYSCALL_DEFINE5(bpf) → bpf_prog_load() → bpf_check() → do_check_insn(); the bug fires on local BPF_LDX BPF_MEMSX/BPF_MEM stack fills in check_mem_access(), not on a remote protocol message.\nAC:L - The attacker writes the instruction sequence; ldsx_fill_scalar_id_not_shared deterministically spills a u32 with bit 31 set, fills it with *(s32*) into r4 and *(u32*) into r5, then uses if r5 == 0x80000000 so sync_linked_regs() poisons r4, with no race or external state.\nPR:L - check_stack_write_fixed_off()/check_stack_read_fixed_off() only preserve spilled scalar ids when env->bpf_capable, set from bpf_token_capable(CAP_BPF) in bpf_check(); unprivileged socket-filter loads therefore miss this path. CAP_BPF is delegable into a user namespace via bpf_token_create(), so this is Low, not init-namespace root.\nUI:N - The attacker loads the crafted program with bpf(BPF_PROG_LOAD), creates the hash map, and triggers bpf_map_lookup_elem plus the MEMSX/MEM fills themselves; no other user must mount media, open a file, or otherwise act.\nS:U - The confused r4 offset is applied to a PTR_TO_MAP_VALUE from bpf_map_lookup_elem() and corrupts host kernel heap in the same security authority; this is a verifier-bypass local privilege escalation, not a KVM/IOMMU guest-to-host crossing.\nC:H - After sync_linked_regs() copies known 0x80000000 onto the sign-extended r4 (runtime 0xffffffff80000000), r4 >>= 63 is believed 0 but is 1, so r0 += r4; *(u8*)(r0+7) on the 8-byte map value is an accepted out-of-bounds kernel read; repeating r0 += r4 yields an arbitrary-length read primitive.\nI:H - The same false r4==0 bound lets the verifier accept a store through that map-value pointer (replace the *(u8*)(r0+7) load with a store); repeating r0 += r4 before the store is an arbitrary kernel heap write usable for control-flow hijacking.\nA:H - The accepted program performs an out-of-bounds access on the bpf_map_lookup_elem() result (the selftest is rejected after the fix with \"R0 max value is outside of the allowed memory range\"); that heap OOB can oops or panic the kernel." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "kernel/bpf/verifier.c" ], "versions": [ { "version": "3cd5c890652ba1f0682adc291b5446245259b692", "lessThan": "f3614622dc41f3dd99bb4f691da253814e4e6cae", "status": "affected", "versionType": "git" }, { "version": "3cd5c890652ba1f0682adc291b5446245259b692", "lessThan": "2cb5f4ca695ebe552647e5ba4aad6934d6a43bae", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "kernel/bpf/verifier.c" ], "versions": [ { "version": "7.0", "status": "affected" }, { "version": "0", "lessThan": "7.0", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.6", "lessThanOrEqual": "7.2.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.3", "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": "7.0", "versionEndExcluding": "7.2.6" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.0", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/f3614622dc41f3dd99bb4f691da253814e4e6cae" }, { "url": "https://git.kernel.org/stable/c/2cb5f4ca695ebe552647e5ba4aad6934d6a43bae" } ], "title": "bpf: Drop scalar id on sign-extending narrowing stack fills", "x_generator": { "engine": "bippy-1.2.0" } } } }