{"id":"CVE-2026-98641","kind":"vulnerability","aliases":["CVE-2026-98641"],"related":[],"title":"Linux kernel arm64 BPF: exception callback can corrupt stack, enabling kernel crash","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nbpf, arm64: set up the frame pointer for the exception callback\n\nA program acting as exception boundary saves all callee-saved registers,\nso build_prologue() takes the exception_cb path and never calls\npush_callee_regs(). That is the only place find_used_callee_regs() runs,\nand with it the only place ctx->fp_used is set, so the callback prologue\ndoes not emit the\n\n  mov x25, sp\n\nthat points BPF_REG_FP at the frame the callback runs on. x25 keeps\nwhatever it held when bpf_throw() was called. If the throw came from a\nsubprogram that uses its own BPF stack, that is the subprogram's frame\npointer, and since the subprogram never returns it never restores x25\neither.\n\nStack accesses through BPF_REG_FP are rewritten to be stack pointer\nrelative, so those still land in the callback's own frame. Materializing\nthe register does not: a callback that passes the address of a local\nvariable to a helper hands over an address in the dead subprogram's\nframe. That address is below the callback's stack pointer by then, and\nthe helper's own call chain covers it, so the helper can write over its\nown return address. 0x1234 below is the value the helper was asked to\nstore:\n\n  pc : 0x1234\n  lr : 0x1234\n  Call trace:\n   0x1234 (P)\n   bpf_test_run+0x188/0x3e0\n   bpf_prog_test_run_skb+0x47c/0x998\n   __sys_bpf+0xbdc/0xdd8\n  Kernel panic - not syncing: Oops: Fatal exception in interrupt\n\nSet ctx->fp_used on the exception callback path so that the existing code\nfurther down sets x25 from the stack pointer. The epilogue restores it\nfrom the main program's save area along with the other callee-saved\nregisters, as it already does. x86 sets the frame pointer for the\ncallback from the argument it is passed, and powerpc computes it from\nthe stack pointer.","summary":"On arm64, a BPF program that throws through a subprogram can leave the frame pointer pointing at a dead stack frame, so a callback passing a local variable address to a helper can overwrite memory in the helper's call chain. The sources describe a kernel panic from this stack corruption; no severity or exploitation details are given.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["arm64","bpf","infrastructure","linux-kernel"],"not_affected_if":["bpf-disabled","powerpc","x86-64"],"how_to_check":"- `uname -r` and compare against the kernel version that contains the fix (unknown from sources)\n- Check whether the system is arm64 (`uname -m` returns `aarch64`) and whether unprivileged or local users can load BPF programs (`sysctl kernel.unprivileged_bpf_disabled`)","fix":"- Update the Linux kernel to a release that includes the upstream commit resolving this issue (fixed versions unknown from sources)","status":"open","published_at":"2026-10-18T16:17:17+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","triaged_at":"2026-10-25T05:20:54+00:00","updated_at":"2026-10-25T05:20:54+00:00","category":"infrastructure","confidence":0.5,"triage":{"at":"2026-10-25T05:20:54Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a release that includes the upstream commit resolving this issue (fixed versions unknown from sources)","reach":"local","title":"Linux kernel arm64 BPF: exception callback can corrupt stack, enabling kernel crash","impact":"medium","summary":"On arm64, a BPF program that throws through a subprogram can leave the frame pointer pointing at a dead stack frame, so a callback passing a local variable address to a helper can overwrite memory in the helper's call chain. The sources describe a kernel panic from this stack corruption; no severity or exploitation details are given.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","arm64","bpf"],"confidence":0.5,"needs_auth":"unknown","worst_case":"Kernel memory corruption and a kernel panic; code execution not stated in sources","analyst_note":"Confirm affected and fixed kernel versions and whether unprivileged BPF loading is required, from the NVD entry and the upstream kernel commit.","how_to_check":"- `uname -r` and compare against the kernel version that contains the fix (unknown from sources)\n- Check whether the system is arm64 (`uname -m` returns `aarch64`) and whether unprivileged or local users can load BPF programs (`sysctl kernel.unprivileged_bpf_disabled`)","needs_analyst":true,"not_affected_if":["x86-64","powerpc","bpf-disabled"],"who_is_affected":"Only arm64 Linux kernels that use BPF programs with exception callbacks (bpf_throw) and subprograms that use their own BPF stack are described as affected. Systems on x86 or powerpc, or on arm64 kernels without BPF exception handling in use, are not described as affected; the sources do not say which kernel versions are impacted.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000719,"input_tokens":3873,"output_tokens":663,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'+0':318C,325C,329C '-2026':14A,17A '-98641':15A,18A '0x1234':296C,308C,310C,313C 'access':216C 'act':106C 'address':53B,248C,259C,267C,295C 'along':373C 'alreadi':383C 'area':372C 'argument':395C 'arm64':3A,19B,26B,94C 'ask':304C 'boundari':109C 'bpf':4A,20B,28B,93C,164C,180C,195C,218C,315C,320C,328C 'build':117C 'call':64B,126C,183C,282C,311C 'callback':6A,48B,103C,153C,171C,234C,244C,271C,347C,392C 'calle':113C,128C,137C,378C 'callee-sav':112C,377C 'came':187C 'cb':122C 'chain':65B,283C 'code':353C 'comput':401C 'corrupt':8A,75B 'cover':284C 'crash':12A 'ctx':146C,341C 'cve':13A,16A 'dead':43B,262C 'describ':68B 'detail':80B 'either':214C 'emit':157C 'enabl':10A 'epilogu':363C 'except':5A,102C,108C,121C,337C,346C 'exist':352C 'exploit':79B 'fatal':336C 'find':135C 'follow':88C 'fp':147C,166C,220C,342C 'frame':38B,45B,98C,169C,202C,237C,265C,388C 'given':82B 'hand':256C 'held':178C 'helper':56B,62B,255C,279C,288C,302C 'infrastructur':21B 'interrupt':339C 'keep':175C 'kernel':2A,11A,24B,70B,86C,331C 'land':231C 'leav':36B 'linux':1A,23B,85C 'linux-kernel':22B 'local':51B,251C 'lr':309C 'main':368C 'materi':238C 'memori':59B 'mov':159C 'never':125C,208C,211C 'oop':335C 'overwrit':58B 'p':314C 'panic':71B,332C 'pass':49B,246C,398C 'path':123C,348C 'pc':307C 'place':134C,145C 'point':40B,163C 'pointer':39B,99C,203C,226C,274C,361C,389C,406C 'powerpc':400C 'prog':321C 'program':29B,105C,369C 'prologu':118C,154C 'push':127C 'reg':129C,138C,165C,219C 'regist':115C,240C,380C 'relat':227C 'resolv':92C 'restor':212C,364C 'return':209C,294C 'rewritten':222C 'run':139C,172C,317C,323C 'save':110C,114C,371C,379C 'set':95C,150C,340C,356C,386C 'sever':77B 'sinc':205C 'skb':324C 'sourc':67B 'sp':161C 'stack':9A,44B,74B,196C,215C,225C,273C,360C,405C 'still':230C 'store':306C 'subprogram':34B,190C,200C,207C,263C 'sync':334C 'sys':327C 'take':119C 'test':316C,322C 'throw':31B,181C,186C 'trace':312C 'use':136C,148C,192C,343C 'valu':300C 'variabl':52B,252C 'vulner':89C 'whatev':176C 'write':290C 'x188/0x3e0':319C 'x25':160C,174C,213C,357C 'x47c/0x998':326C 'x86':385C 'xbdc/0xdd8':330C","nicknames":[],"mitigations":[],"who_affected":"Only arm64 Linux kernels that use BPF programs with exception callbacks (bpf_throw) and subprograms that use their own BPF stack are described as affected. Systems on x86 or powerpc, or on arm64 kernels without BPF exception handling in use, are not described as affected; the sources do not say which kernel versions are impacted.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:17+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98641","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98641","severity":null,"published_at":"2026-10-18T16:17:17+00:00","modified_at":"2026-10-19T10:19:28+00:00","first_seen_at":"2026-10-23T21:57:16+00:00","fetched_at":"2026-10-23T22:28:56+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}