{"id":"CVE-2026-120326","kind":"vulnerability","aliases":["CVE-2026-120326"],"related":[],"title":"Vaadin Flow: download file names let attackers pick saved file extension","description":"DownloadEvent.setFileName(String) in Vaadin Flow writes the download file name into the Content-Disposition header without escaping it. When the name is pure US-ASCII the header is built as attachment; filename=\"<name>\" with the name inserted verbatim, so a double quote in the name ends the quoted string early and the rest of the name is read by the browser as further header parameters. The inline(String) variant, present from Vaadin 25.0, builds the name the same way. An application that passes an untrusted file name to either method, for example when re-serving a file under the name it was uploaded with, lets an attacker add a filename* parameter. Browsers prefer filename* over filename, so the file is saved under a name and extension of the attacker's choosing, which defeats any file name or extension restriction the application enforces. The attacker cannot change the attachment or inline disposition itself and cannot split the header.\n\nUsers of affected versions should apply the following mitigation or upgrade. Releases that have fixed this issue include:\n\nProduct version\nVaadin 24.8.0 - 24.8.17\nVaadin 24.9.0 - 24.9.25\nVaadin 24.10.0 - 24.10.13\nVaadin 25.0.0 - 25.0.13\nVaadin 25.1.0 - 25.1.13\nVaadin 25.2.0 - 25.2.12\nVaadin 25.3.0 - 25.3.4\n\nMitigation\nNo fixed release on this line, upgrade to 24.9.26 or newer\nUpgrade to 24.9.26\nUpgrade to 24.10.14\nNo fixed release on this line, upgrade to 25.2.13 or newer\nNo fixed release on this line, upgrade to 25.2.13 or newer\nUpgrade to 25.2.13\nUpgrade to 25.3.5\n\nVaadin versions below 24.8 are not affected: the DownloadEvent API does not exist in them.","summary":"Vaadin Flow's DownloadEvent.setFileName and inline methods do not escape the download file name in the Content-Disposition header. An attacker who controls a file name the application serves can add a filename* parameter, so browsers save the file under a name and extension the attacker chooses.","severity":"medium","cvss":4.8,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["file-download","java","package","vaadin","vaadin-flow"],"not_affected_if":["fixed-version","no-download-api","server-generated-file-names"],"how_to_check":"- Check the Vaadin Flow version in the project build file (pom.xml or build.gradle) for `com.vaadin` dependencies.\n- Search the application code for calls to `DownloadEvent.setFileName(` or `inline(` that pass user-supplied file names.\n- Versions in the affected ranges: `24.8.0` to `24.8.17`, `24.9.0` to `24.9.25`, `24.10.0` to `24.10.13`, `25.0.0` to `25.0.13`, `25.1.0` to `25.1.13`, `25.2.0` to `25.2.12`, `25.3.0` to `25.3.4`.","fix":"- Vaadin 24.9: upgrade to `24.9.26`\n- Vaadin 24.10: upgrade to `24.10.14`\n- Vaadin 25.2: upgrade to `25.2.13`\n- Vaadin 25.3: upgrade to `25.3.5`","status":"open","published_at":"2026-11-10T12:17:16+00:00","first_seen_at":"2026-11-10T12:21:53+00:00","triaged_at":"2026-11-10T12:22:49+00:00","updated_at":"2026-11-10T12:22:49+00:00","category":"package","confidence":0.75,"triage":{"at":"2026-11-10T12:22:49Z","model":"claude-haiku-5-5","output":{"fix":"- Vaadin 24.9: upgrade to `24.9.26`\n- Vaadin 24.10: upgrade to `24.10.14`\n- Vaadin 25.2: upgrade to `25.2.13`\n- Vaadin 25.3: upgrade to `25.3.5`","reach":"internet","title":"Vaadin Flow: download file names let attackers pick saved file extension","impact":"low","summary":"Vaadin Flow's DownloadEvent.setFileName and inline methods do not escape the download file name in the Content-Disposition header. An attacker who controls a file name the application serves can add a filename* parameter, so browsers save the file under a name and extension the attacker chooses.","audience":"businesses","category":"package","nicknames":[],"who_cares":["vaadin","java","vaadin-flow","file-download"],"confidence":0.75,"fix_status":"available","needs_auth":"unknown","worst_case":"Attacker controls saved file name and extension, bypassing extension restrictions","analyst_note":"","how_to_check":"- Check the Vaadin Flow version in the project build file (pom.xml or build.gradle) for `com.vaadin` dependencies.\n- Search the application code for calls to `DownloadEvent.setFileName(` or `inline(` that pass user-supplied file names.\n- Versions in the affected ranges: `24.8.0` to `24.8.17`, `24.9.0` to `24.9.25`, `24.10.0` to `24.10.13`, `25.0.0` to `25.0.13`, `25.1.0` to `25.1.13`, `25.2.0` to `25.2.12`, `25.3.0` to `25.3.4`.","plain_action":"","product_name":"","needs_analyst":false,"not_affected_if":["fixed-version","server-generated-file-names","no-download-api"],"who_is_affected":"Applications built with Vaadin Flow that pass an untrusted file name to DownloadEvent.setFileName or the inline method, for example when re-serving an uploaded file under its original name, are exposed. Versions below 24.8 are not affected because the API does not exist there, and applications that only serve files under names they generate themselves are not meaningfully exposed.","user_interaction":"yes","product_ecosystem":"","needs_special_setup":"unknown","severity_if_unknown":"unknown"},"cost_usd":0.000911,"input_tokens":5089,"output_tokens":804,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-120326':14A,17A '-2026':13A,16A '24.10.0':261C '24.10.13':262C '24.10.14':292C '24.8':324C '24.8.0':255C '24.8.17':256C '24.9.0':258C '24.9.25':259C '24.9.26':284C,289C '25.0':148C '25.0.0':264C '25.0.13':265C '25.1.0':267C '25.1.13':268C '25.2.0':270C '25.2.12':271C '25.2.13':301C,312C,317C '25.3.0':273C '25.3.4':274C '25.3.5':320C 'add':58B,184C 'affect':236C,327C 'api':330C 'appli':239C 'applic':55B,156C,217C 'ascii':101C 'attach':107C,224C 'attack':7A,48B,73B,183C,205C,220C 'browser':63B,136C,188C 'build':149C 'built':105C 'cannot':221C,230C 'chang':222C 'choos':74B,207C 'content':44B,88C 'content-disposit':43B,87C 'control':50B 'cve':12A,15A 'defeat':209C 'disposit':45B,89C,227C 'doubl':116C 'download':3A,20B,38B,82C 'downloadev':329C 'downloadevent.setfilename':30B,75C 'earli':125C 'either':164C 'end':121C 'enforc':218C 'escap':36B,92C 'exampl':167C 'exist':333C 'extens':11A,71B,202C,214C 'file':4A,10A,19B,39B,52B,66B,83C,161C,173C,195C,211C 'file-download':18B 'filenam':60B,108C,186C,190C,192C 'fix':248C,277C,294C,305C 'flow':2A,26B,28B,79C 'follow':241C 'header':46B,90C,103C,139C,233C 'includ':251C 'inlin':32B,142C,226C 'insert':112C 'issu':250C 'java':21B 'let':6A,181C 'line':281C,298C,309C 'method':33B,165C 'mitig':242C,275C 'name':5A,40B,53B,69B,84C,96C,111C,120C,131C,151C,162C,176C,200C,212C 'newer':286C,303C,314C 'packag':22B 'paramet':61B,140C,187C 'pass':158C 'pick':8A 'prefer':189C 'present':145C 'product':252C 'pure':98C 'quot':117C,123C 're':170C 're-serv':169C 'read':133C 'releas':245C,278C,295C,306C 'rest':128C 'restrict':215C 'save':9A,64B,197C 'serv':56B,171C 'split':231C 'string':76C,124C,143C 'untrust':160C 'upgrad':244C,282C,287C,290C,299C,310C,315C,318C 'upload':179C 'us':100C 'us-ascii':99C 'user':234C 'vaadin':1A,23B,25B,27B,78C,147C,254C,257C,260C,263C,266C,269C,272C,321C 'vaadin-flow':24B 'variant':144C 'verbatim':113C 'version':237C,253C,322C 'way':154C 'without':91C 'write':80C","nicknames":[],"mitigations":[],"who_affected":"Applications built with Vaadin Flow that pass an untrusted file name to DownloadEvent.setFileName or the inline method, for example when re-serving an uploaded file under its original name, are exposed. Versions below 24.8 are not affected because the API does not exist there, and applications that only serve files under names they generate themselves are not meaningfully exposed.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["filedownload","java","medium","package","vaadin","vaadinflow"],"campaign_type":null,"search_a":"'-120326':14A,17A '-2026':13A,16A 'attack':7A 'cve':12A,15A 'download':3A 'extens':11A 'file':4A,10A 'flow':2A 'let':6A 'name':5A 'pick':8A 'save':9A 'vaadin':1A","search_b":"'add':58B 'applic':55B 'attack':48B,73B 'browser':63B 'choos':74B 'content':44B 'content-disposit':43B 'control':50B 'disposit':45B 'download':20B,38B 'downloadevent.setfilename':30B 'escap':36B 'extens':71B 'file':19B,39B,52B,66B 'file-download':18B 'filenam':60B 'flow':26B,28B 'header':46B 'inlin':32B 'java':21B 'method':33B 'name':40B,53B,69B 'packag':22B 'paramet':61B 'save':64B 'serv':56B 'vaadin':23B,25B,27B 'vaadin-flow':24B","search_c":"'24.10.0':261C '24.10.13':262C '24.10.14':292C '24.8':324C '24.8.0':255C '24.8.17':256C '24.9.0':258C '24.9.25':259C '24.9.26':284C,289C '25.0':148C '25.0.0':264C '25.0.13':265C '25.1.0':267C '25.1.13':268C '25.2.0':270C '25.2.12':271C '25.2.13':301C,312C,317C '25.3.0':273C '25.3.4':274C '25.3.5':320C 'add':184C 'affect':236C,327C 'api':330C 'appli':239C 'applic':156C,217C 'ascii':101C 'attach':107C,224C 'attack':183C,205C,220C 'browser':136C,188C 'build':149C 'built':105C 'cannot':221C,230C 'chang':222C 'choos':207C 'content':88C 'content-disposit':87C 'defeat':209C 'disposit':89C,227C 'doubl':116C 'download':82C 'downloadev':329C 'downloadevent.setfilename':75C 'earli':125C 'either':164C 'end':121C 'enforc':218C 'escap':92C 'exampl':167C 'exist':333C 'extens':202C,214C 'file':83C,161C,173C,195C,211C 'filenam':108C,186C,190C,192C 'fix':248C,277C,294C,305C 'flow':79C 'follow':241C 'header':90C,103C,139C,233C 'includ':251C 'inlin':142C,226C 'insert':112C 'issu':250C 'let':181C 'line':281C,298C,309C 'method':165C 'mitig':242C,275C 'name':84C,96C,111C,120C,131C,151C,162C,176C,200C,212C 'newer':286C,303C,314C 'paramet':140C,187C 'pass':158C 'prefer':189C 'present':145C 'product':252C 'pure':98C 'quot':117C,123C 're':170C 're-serv':169C 'read':133C 'releas':245C,278C,295C,306C 'rest':128C 'restrict':215C 'save':197C 'serv':171C 'split':231C 'string':76C,124C,143C 'untrust':160C 'upgrad':244C,282C,287C,290C,299C,310C,315C,318C 'upload':179C 'us':100C 'us-ascii':99C 'user':234C 'vaadin':78C,147C,254C,257C,260C,263C,266C,269C,272C,321C 'variant':144C 'verbatim':113C 'version':237C,253C,322C 'way':154C 'without':91C 'write':80C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-11-10T12:17:16+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:A/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","cvss_by":"security@vaadin.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-120326","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-120326","severity":null,"published_at":"2026-11-10T12:17:16+00:00","modified_at":"2026-11-10T12:17:16+00:00","first_seen_at":"2026-11-10T12:21:53+00:00","fetched_at":"2026-11-10T12:21:53+00:00","note":null}],"documents":[],"disclosures":[],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}