{"id":"CVE-2026-99059","kind":"vulnerability","aliases":["CVE-2026-99059"],"related":[],"title":"Linux kernel WireGuard: duplicate handshake response can start a second session","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nwireguard: noise: reject response consumption after intermediate initiation\n\nTwo threads begin processing the identical response message, received\ntwice. The first thread, A, runs. While it's running, the second one,\nB, gets partway through, and during that slow calculation, or even while\nblocking on down_write(), A completes and then also a handshake\ninitiation that's already been queued up runs in thread C, which itself\ntakes that same down_write(). The handshake initiation creation\nsucceeds, and sets the state back to waiting-for-response, and calls\nup_write(), at which point thread B resumes, because either its finished\nits calculations or was finally allowed to acquire down_write(). Thread\nB then copies the state back to the peer, and begins a new session,\nusing that state, which is the same session as the one made in thread A.\n\nThread A\t\t\tThread B\t\t\tThread C\n\ndown_read()\n sA = handshake->state\n memcpy(cA, handshake->crypto)\nup_read()\nif (sA != 1)\n goto fail\nslow_crypto(cA)\n\t\t\t\tdown_read()\n\t\t\t\t sB = handshake->state\n\t\t\t\t memcpy(cB, handshake->crypto)\n\t\t\t\tup_read()\n\t\t\t\tif (sB != 1)\n\t\t\t\t goto fail\n\t\t\t\tslow_crypto(cB)\ndown_write()\n if (sA != handshake->state)\n  goto fail\n memcpy(handshake->crypto, cA)\n handshake->state = 2\nup_write()\ndown_write()\n if (handshake->state != 2)\n  goto fail\n derive_session(handshake->crypto)\nup_write()\n\t\t\t\t\t\t\t\tdown_write()\n\t\t\t\t\t\t\t\t slow_crypto(handshake->crypto)\n\t\t\t\t\t\t\t\t handshake->state = 1\n\t\t\t\t\t\t\t\tup_write()\n\t\t\t\tdown_write()\n\t\t\t\t if (sB != handshake->state)\n\t\t\t\t   goto fail\n\t\t\t\t memcpy(handshake->crypto, cB)\n\t\t\t\t handshake->state = 2\n\t\t\t\tup_write()\n\t\t\t\tdown_write()\n\t\t\t\t if (handshake->state != 2)\n\t\t\t\t  goto fail\n\t\t\t\t derive_session(handshake->crypto)\n\t\t\t\tup_write()\n\nThis seems basically impossible to hit in a meaningful way in practice,\nbut ensure that it absolutely cannot happen by comparing the ephemeral\nprivate key that's on the stack with the latest one that the peer's\nhandshake state has.","summary":"A race in the Linux kernel's WireGuard noise handshake lets a duplicated handshake response be consumed after a newer initiation has already run, so two threads can derive the same session. The sources do not say what an attacker gains beyond a reused session state.","severity":"unknown","cvss":null,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["linux-kernel","runtime","self-hosted","wireguard"],"not_affected_if":["no-wireguard"],"how_to_check":"- `uname -r` and compare against the fixed kernel builds listed by your distribution\n- `lsmod | grep wireguard` or `modinfo wireguard` to confirm WireGuard is loaded or built in\n- unknown whether a specific kernel version is affected","fix":"- Update the Linux kernel to a build that includes the upstream fix for this WireGuard noise change; the exact fixed version is unknown from the sources\n- Check your distribution's kernel advisory for the patched package","status":"open","published_at":"2026-10-23T13:17:29+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","triaged_at":"2026-10-25T04:53:56+00:00","updated_at":"2026-10-25T04:53:56+00:00","category":"runtime","confidence":0.4,"triage":{"at":"2026-10-25T04:53:56Z","model":"claude-haiku-5-5","output":{"fix":"- Update the Linux kernel to a build that includes the upstream fix for this WireGuard noise change; the exact fixed version is unknown from the sources\n- Check your distribution's kernel advisory for the patched package","reach":"network","title":"Linux kernel WireGuard: duplicate handshake response can start a second session","impact":"low","summary":"A race in the Linux kernel's WireGuard noise handshake lets a duplicated handshake response be consumed after a newer initiation has already run, so two threads can derive the same session. The sources do not say what an attacker gains beyond a reused session state.","category":"runtime","nicknames":[],"who_cares":["linux-kernel","wireguard","self-hosted"],"confidence":0.4,"needs_auth":"unknown","worst_case":"unknown; sources say a duplicate session state is reused","analyst_note":"Find the kernel commit and fixed stable versions for this NVD entry; the sources give no CVSS or exploitation details.","how_to_check":"- `uname -r` and compare against the fixed kernel builds listed by your distribution\n- `lsmod | grep wireguard` or `modinfo wireguard` to confirm WireGuard is loaded or built in\n- unknown whether a specific kernel version is affected","needs_analyst":true,"not_affected_if":["no-wireguard"],"who_is_affected":"Systems running a Linux kernel with WireGuard enabled, whether built in or loaded as a module, are in scope. The sources describe a timing race that requires duplicate handshake responses, and say it is very hard to hit in practice. Systems without WireGuard can skip it.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"unknown"},"cost_usd":0.000692,"input_tokens":3961,"output_tokens":592,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':13A,16A '-99059':14A,17A '1':241C,260C,305C '2':280C,288C,322C,330C 'absolut':355C 'acquir':189C 'allow':187C 'alreadi':48B,138C 'also':132C 'attack':65B 'b':112C,176C,193C,225C 'back':162C,198C 'basic':341C 'begin':92C,203C 'beyond':67B 'block':124C 'c':145C,227C 'ca':234C,246C,277C 'calcul':120C,183C 'call':169C 'cannot':356C 'cb':253C,265C,319C 'compar':359C 'complet':129C 'consum':42B 'consumpt':86C 'copi':195C 'creation':156C 'crypto':236C,245C,255C,264C,276C,294C,300C,302C,318C,336C 'cve':12A,15A 'deriv':54B,291C,333C 'duplic':4A,38B 'either':179C 'ensur':352C 'ephemer':361C 'even':122C 'fail':243C,262C,273C,290C,315C,332C 'final':186C 'finish':181C 'first':101C 'follow':77C 'gain':66B 'get':113C 'goto':242C,261C,272C,289C,314C,331C 'handshak':5A,35B,39B,134C,154C,231C,235C,250C,254C,270C,275C,278C,286C,293C,301C,303C,312C,317C,320C,328C,335C,377C 'happen':357C 'hit':344C 'host':24B 'ident':95C 'imposs':342C 'initi':46B,89C,135C,155C 'intermedi':88C 'kernel':2A,20B,31B,75C 'key':363C 'latest':371C 'let':36B 'linux':1A,19B,30B,74C 'linux-kernel':18B 'made':218C 'meaning':347C 'memcpi':233C,252C,274C,316C 'messag':97C 'new':205C 'newer':45B 'nois':34B,83C 'one':111C,217C,372C 'partway':114C 'peer':201C,375C 'point':174C 'practic':350C 'privat':362C 'process':93C 'queu':140C 'race':27B 'read':229C,238C,248C,257C 'receiv':98C 'reject':84C 'resolv':81C 'respons':6A,40B,85C,96C,167C 'resum':177C 'reus':69B 'run':49B,104C,108C,142C 'runtim':21B 'sa':230C,240C,269C 'say':62B 'sb':249C,259C,311C 'second':10A,110C 'seem':340C 'self':23B 'self-host':22B 'session':11A,57B,70B,206C,214C,292C,334C 'set':159C 'slow':119C,244C,263C,299C 'sourc':59B 'stack':368C 'start':8A 'state':71B,161C,197C,209C,232C,251C,271C,279C,287C,304C,313C,321C,329C,378C 'succeed':157C 'take':148C 'thread':52B,91C,102C,144C,175C,192C,220C,222C,224C,226C 'twice':99C 'two':51B,90C 'use':207C 'vulner':78C 'wait':165C 'waiting-for-respons':164C 'way':348C 'wireguard':3A,25B,33B,82C 'write':127C,152C,171C,191C,267C,282C,284C,296C,298C,307C,309C,324C,326C,338C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with WireGuard enabled, whether built in or loaded as a module, are in scope. The sources describe a timing race that requires duplicate handshake responses, and say it is very hard to hit in practice. Systems without WireGuard can skip it.","tier":"C","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-10-23T13:17:29+00:00","kev":null,"cvss_vector":null,"cvss_by":null,"poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-99059","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-99059","severity":null,"published_at":"2026-10-23T13:17:29+00:00","modified_at":"2026-10-23T13:17:29+00:00","first_seen_at":"2026-10-23T21:57:33+00:00","fetched_at":"2026-10-23T22:29:03+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"}