{"id":"CVE-2026-98505","kind":"vulnerability","aliases":["CVE-2026-98505"],"related":[],"title":"Linux kernel: DAMON hugetlb pages can lose hardware dirty-bit updates","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nmm/damon/vaddr: avoid hw-driven pte updates during damon_hugetlb_mkold()\n\ndamon_hugetlb_mkold() reads the page table entry into a local variable,\nunsets the accessed bit in the variable, and updates the page table entry\nwith the updated variable value.  If hardware updates the same page table\nentry in parallel, the hw updates could be lost.  For example,\nhardware-updated dirty bits might be lost.\n\nAvoid the parallel updates by clearing the page table entry when reading\nit together, using huge_ptep_get_and_clear().  If a parallel write to the\nmemory is made after the clearing, the hw will see the page table entry is\ncleared, trigger page fault and wait until it is handled.  The page fault\nhandling will wait for damon_hugetlb_mkold() due to the page table lock.\n\nBecause hugetlbfs is an in-memory file system and hugetlb pages cannot be\nreclaimed, no critical issue is expected to my best knowledge.  But\ndefinitely this is a nasty bug that should be fixed sooner rather than\nlater.\n\nThe issue was discovered [1] by Sashiko.","summary":"In the Linux kernel's DAMON memory monitor, clearing the accessed bit on hugetlb pages could overwrite hardware-set dirty bits during a race. The sources describe this as a data-integrity bug with no confirmed security impact.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["damon","hugetlb","linux-kernel","runtime"],"not_affected_if":["damon-disabled","no-hugetlb-monitoring"],"how_to_check":"- `uname -r` to see the running kernel version\n- unknown whether DAMON hugetlb monitoring is enabled on the system; the sources do not say how to check","fix":"- Move to a kernel build that includes the upstream fix for mm/damon/vaddr hugetlb handling (the sources do not list fixed versions)","status":"open","published_at":"2026-10-18T16:17:01+00:00","first_seen_at":"2026-10-23T21:57:15+00:00","triaged_at":"2026-10-25T05:25:29+00:00","updated_at":"2026-10-25T05:25:29+00:00","category":"runtime","confidence":0.5,"triage":{"at":"2026-10-25T05:25:29Z","model":"claude-haiku-5-5","output":{"fix":"- Move to a kernel build that includes the upstream fix for mm/damon/vaddr hugetlb handling (the sources do not list fixed versions)","reach":"local","title":"Linux kernel: DAMON hugetlb pages can lose hardware dirty-bit updates","impact":"low","summary":"In the Linux kernel's DAMON memory monitor, clearing the accessed bit on hugetlb pages could overwrite hardware-set dirty bits during a race. The sources describe this as a data-integrity bug with no confirmed security impact.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","damon","hugetlb"],"confidence":0.5,"needs_auth":"unknown","worst_case":"hardware-set dirty bits lost, causing silent data-integrity issues","analyst_note":"Check the upstream kernel commit and NVD entry for affected and fixed kernel versions and whether DAMON is enabled by default.","how_to_check":"- `uname -r` to see the running kernel version\n- unknown whether DAMON hugetlb monitoring is enabled on the system; the sources do not say how to check","needs_analyst":true,"not_affected_if":["damon-disabled","no-hugetlb-monitoring"],"who_is_affected":"Only systems running a Linux kernel with DAMON enabled and monitoring hugetlb-backed memory are exposed. The sources do not say which kernel versions are affected or whether the default configuration enables DAMON. Systems that do not use DAMON can skip it.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"low"},"cost_usd":0.000642,"input_tokens":3613,"output_tokens":561,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':14A,17A '-98505':15A,18A '1':252C 'access':35B,100C 'avoid':76C,142C 'best':231C 'bit':11A,36B,46B,101C,138C 'bug':59B,239C 'cannot':221C 'clear':33B,147C,161C,173C,183C 'confirm':62B 'could':40B,129C 'critic':225C 'cve':13A,16A 'damon':3A,19B,30B,83C,86C,200C 'data':57B 'data-integr':56B 'definit':234C 'describ':52B 'dirti':10A,45B,137C 'dirty-bit':9A 'discov':251C 'driven':79C 'due':203C 'entri':93C,110C,123C,151C,181C 'exampl':133C 'expect':228C 'fault':186C,195C 'file':216C 'fix':243C 'follow':70C 'get':159C 'handl':192C,196C 'hardwar':8A,43B,117C,135C 'hardware-set':42B 'hardware-upd':134C 'huge':157C 'hugetlb':4A,20B,38B,84C,87C,201C,219C 'hugetlbf':210C 'hw':78C,127C,175C 'hw-driven':77C 'impact':64B 'in-memori':213C 'integr':58B 'issu':226C,249C 'kernel':2A,23B,28B,68C 'knowledg':232C 'later':247C 'linux':1A,22B,27B,67C 'linux-kernel':21B 'local':96C 'lock':208C 'lose':7A 'lost':131C,141C 'made':170C 'memori':31B,168C,215C 'might':139C 'mkold':85C,88C,202C 'mm/damon/vaddr':75C 'monitor':32B 'nasti':238C 'overwrit':41B 'page':5A,39B,91C,108C,121C,149C,179C,185C,194C,206C,220C 'parallel':125C,144C,164C 'pte':80C 'ptep':158C 'race':49B 'rather':245C 'read':89C,153C 'reclaim':223C 'resolv':74C 'runtim':24B 'sashiko':254C 'secur':63B 'see':177C 'set':44B 'sooner':244C 'sourc':51B 'system':217C 'tabl':92C,109C,122C,150C,180C,207C 'togeth':155C 'trigger':184C 'unset':98C 'updat':12A,81C,106C,113C,118C,128C,136C,145C 'use':156C 'valu':115C 'variabl':97C,104C,114C 'vulner':71C 'wait':188C,198C 'write':165C","nicknames":[],"mitigations":[],"who_affected":"Only systems running a Linux kernel with DAMON enabled and monitoring hugetlb-backed memory are exposed. The sources do not say which kernel versions are affected or whether the default configuration enables DAMON. Systems that do not use DAMON can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-18T16:17:01+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-98505","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-98505","severity":null,"published_at":"2026-10-18T16:17:01+00:00","modified_at":"2026-10-21T13:21:32+00:00","first_seen_at":"2026-10-23T21:57:15+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"}