{ "dataType": "CVE_RECORD", "dataVersion": "5.2", "cveMetadata": { "cveId": "CVE-2026-99018", "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "state": "PUBLISHED", "assignerShortName": "Linux", "dateReserved": "2026-09-25T10:25:14.386Z", "datePublished": "2026-10-23T12:20:54.888Z", "dateUpdated": "2026-10-24T14:10:05.883Z" }, "containers": { "cna": { "providerMetadata": { "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "shortName": "Linux", "dateUpdated": "2026-10-24T14:10:05.883Z" }, "descriptions": [ { "lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nriscv: entry: gate shadow call stack reload on sstatus.SPP, not tp\n\nUnder CONFIG_SHADOW_CALL_STACK, handle_exception() reloads the kernel\nshadow call stack pointer (gp) only when the trap came from userspace.\nIt made that decision with scs_load_current_if_task_changed, which\ncompares the trap-time tp (read back from sscratch into s5) against the\ncurrent tp:\n\n\tbeq\t\\prev, tp, _skip_scs\n\tscs_load_current\n_skip_scs:\n\ntp is a user-writable register. A user task that sets tp to the\nlinear-map address of its own task_struct (¤t) before trapping\nmakes the comparison succeed (can achieve by brute force with KASLR\nenable under our test), so the kernel skips scs_load_current and\nkeeps running with the gp that userspace left in place. Under\nCONFIG_SHADOW_CALL_STACK gp is the shadow call stack pointer and\nload_global_pointer is a no-op, so the compiler-emitted\n\"sd ra, -8(gp)\" / \"ld ra, -8(gp)\" in every non-leaf function then write\nto, and return through, an attacker-controlled address -- an\nunprivileged kernel arbitrary-write and control-flow-hijack primitive.\nThe poisoned gp is saved to task_struct.scs_sp on return, so the reload\nis skipped on every subsequent entry as well.\n\nDecide \"came from userspace\" from the hardware sstatus.SPP bit (already\nin s1 at this point) instead of from tp, mirroring the check that\nret_from_exception already uses a few instructions later. SPP is\nwritten by hardware on trap entry and cannot be forged from U-mode.\nLegitimate behaviour is unchanged: user entries (SPP=0) reload the task\nshadow call stack, nested kernel entries (SPP=1) skip it." } ], "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 - A U-mode RISC-V task controls the ordinary tp/gp registers and executes ecall; stvec enters handle_exception(), whose scs_load_current_if_task_changed macro consumes those values before do_trap_ecall_u. No wire or physical device carries the causal data.\nAC:L - On a CONFIG_SHADOW_CALL_STACK kernel, wrong tp guesses simply invoke scs_load_current, while a match to ¤t skips it; the fix explicitly reports successfully brute-forcing that match with KASLR enabled. No race or victim-controlled state is required.\nPR:L - The vulnerable comparison occurs in handle_exception() before do_trap_ecall_u reaches syscall_enter_from_user_mode_randomize_stack() or any syscall permission check; U-mode may write tp/gp and execute ecall without capabilities.\nUI:N - After the attacker's own ecall poisons gp, ret_from_exception saves it into task_struct.scs_sp; no victim must open, mount, approve, or race anything.\nS:U - The forged SCS pointer pivots execution inside the same Linux kernel that handles the caller's ecall; the path crosses no KVM guest-host or IOMMU security authority.\nC:H - Because load_global_pointer is a no-op, attacker-selected gp controls compiler SCS loads such as ld ra,-8(gp); the resulting supervisor-mode control-flow hijack permits arbitrary kernel-memory disclosure.\nI:H - Compiler SCS stores such as sd ra,-8(gp) write through the attacker-selected gp to a chosen kernel address, and the corresponding return-address control enables arbitrary kernel code execution.\nA:H - The attacker can direct the SCS store/load at invalid or critical kernel memory from do_trap_ecall_u, causing a supervisor fault, corrupted control flow, and kernel oops or panic." } ] } ], "affected": [ { "product": "Linux", "vendor": "Linux", "defaultStatus": "unaffected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/riscv/include/asm/scs.h", "arch/riscv/kernel/entry.S" ], "versions": [ { "version": "d1584d791a297aa8ed93503382a682a6ecfc4218", "lessThan": "6639735367a7d491977e9e5e7afc50b489d81d83", "status": "affected", "versionType": "git" }, { "version": "d1584d791a297aa8ed93503382a682a6ecfc4218", "lessThan": "7d1367a53137e379498eb8791295e58854378636", "status": "affected", "versionType": "git" }, { "version": "d1584d791a297aa8ed93503382a682a6ecfc4218", "lessThan": "37b4401ee6fa06046446d55e97e8d11784080843", "status": "affected", "versionType": "git" }, { "version": "d1584d791a297aa8ed93503382a682a6ecfc4218", "lessThan": "4d0697f192975dab5985e921989be1d85cf580e9", "status": "affected", "versionType": "git" } ] }, { "product": "Linux", "vendor": "Linux", "defaultStatus": "affected", "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git", "programFiles": [ "arch/riscv/include/asm/scs.h", "arch/riscv/kernel/entry.S" ], "versions": [ { "version": "6.7", "status": "affected" }, { "version": "0", "lessThan": "6.7", "status": "unaffected", "versionType": "semver" }, { "version": "6.12.113", "lessThanOrEqual": "6.12.*", "status": "unaffected", "versionType": "semver" }, { "version": "6.18.57", "lessThanOrEqual": "6.18.*", "status": "unaffected", "versionType": "semver" }, { "version": "7.2.11", "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": "6.7", "versionEndExcluding": "6.12.113" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "6.18.57" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "7.2.11" }, { "vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.7", "versionEndExcluding": "7.3" } ] } ] } ], "references": [ { "url": "https://git.kernel.org/stable/c/6639735367a7d491977e9e5e7afc50b489d81d83" }, { "url": "https://git.kernel.org/stable/c/7d1367a53137e379498eb8791295e58854378636" }, { "url": "https://git.kernel.org/stable/c/37b4401ee6fa06046446d55e97e8d11784080843" }, { "url": "https://git.kernel.org/stable/c/4d0697f192975dab5985e921989be1d85cf580e9" } ], "title": "riscv: entry: gate shadow call stack reload on sstatus.SPP, not tp", "x_generator": { "engine": "bippy-1.2.0" } } } }