{"id":"CVE-2026-74857","kind":"vulnerability","aliases":["CVE-2026-74857"],"related":[],"title":"Synology DSM: Auth API flaw lets logged-in users read or write files","description":"A missing critical step in authentication vulnerability in the Auth API in Synology DiskStation Manager (DSM) before 7.3.2-86009-5 and 7.4.1-90080-1 allows remote authenticated users to read or write arbitrary files and conduct denial-of-service attacks.","summary":"Synology DiskStation Manager has a missing authentication step in its Auth API, so a remote user who already has an account can read or write arbitrary files on the NAS. The same flaw can also be used to knock the device offline with denial-of-service attacks.","severity":"high","cvss":8.8,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["dsm","infrastructure","nas","self-hosted","synology"],"not_affected_if":["no-remote-access","patched-dsm-version"],"how_to_check":"- Check the DSM version under Control Panel > Info Center; compare it with the fixed versions listed below.\n- Confirm whether remote access to DSM is exposed to the internet, for example through QuickConnect or a port forward.","fix":"- DSM `7.3.2-86009-5` or later for the 7.3 branch\n- DSM `7.4.1-90080-1` or later for the 7.4 branch","status":"open","published_at":"2026-11-12T04:17:20+00:00","first_seen_at":"2026-11-12T04:47:09+00:00","triaged_at":"2026-11-12T04:47:36+00:00","updated_at":"2026-11-12T04:47:36+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-11-12T04:47:36Z","model":"claude-haiku-5-5","output":{"fix":"- DSM `7.3.2-86009-5` or later for the 7.3 branch\n- DSM `7.4.1-90080-1` or later for the 7.4 branch","reach":"network","title":"Synology DSM: Auth API flaw lets logged-in users read or write files","impact":"high","summary":"Synology DiskStation Manager has a missing authentication step in its Auth API, so a remote user who already has an account can read or write arbitrary files on the NAS. The same flaw can also be used to knock the device offline with denial-of-service attacks.","audience":"businesses","category":"infrastructure","nicknames":[],"who_cares":["synology","dsm","nas","self-hosted"],"confidence":0.6,"fix_status":"available","needs_auth":"yes","worst_case":"Attacker reads or overwrites arbitrary files and can crash the NAS.","analyst_note":"Confirm from the Synology security advisory whether the fix applies to the 7.3 and 7.4 branches and whether the DoS impact needs any specific service enabled.","how_to_check":"- Check the DSM version under Control Panel > Info Center; compare it with the fixed versions listed below.\n- Confirm whether remote access to DSM is exposed to the internet, for example through QuickConnect or a port forward.","plain_action":"","product_name":"","needs_analyst":true,"not_affected_if":["patched-dsm-version","no-remote-access"],"who_is_affected":"Any Synology NAS running DiskStation Manager below the fixed versions is in scope. Exposure is greatest where DSM is reachable from the internet, since the attacker must first hold a valid user account on the device. Devices that are not running DSM, or that are patched to the fixed builds, can skip this.","user_interaction":"no","product_ecosystem":"","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000776,"input_tokens":4552,"output_tokens":642,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-1':99C '-2026':16A,19A '-5':95C '-74857':17A,20A '-86009':94C '-90080':98C '7.3.2':93C '7.4.1':97C 'account':48B 'allow':100C 'alreadi':45B 'also':62B 'api':4A,39B,86C 'arbitrari':53B,108C 'attack':75B,116C 'auth':3A,38B,85C 'authent':34B,81C,102C 'conduct':111C 'critic':78C 'cve':15A,18A 'denial':72B,113C 'denial-of-servic':71B,112C 'devic':68B 'diskstat':29B,89C 'dsm':2A,21B,91C 'file':14A,54B,109C 'flaw':5A,60B 'host':26B 'infrastructur':22B 'knock':66B 'let':6A 'log':8A 'logged-in':7A 'manag':30B,90C 'miss':33B,77C 'nas':23B,57B 'offlin':69B 'read':11A,50B,105C 'remot':42B,101C 'self':25B 'self-host':24B 'servic':74B,115C 'step':35B,79C 'synolog':1A,27B,28B,88C 'use':64B 'user':10A,43B,103C 'vulner':82C 'write':13A,52B,107C","nicknames":[],"mitigations":[],"who_affected":"Any Synology NAS running DiskStation Manager below the fixed versions is in scope. Exposure is greatest where DSM is reachable from the internet, since the attacker must first hold a valid user account on the device. Devices that are not running DSM, or that are patched to the fixed builds, can skip this.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["dsm","high","infrastructure","nas","selfhosted","synology"],"campaign_type":null,"search_a":"'-2026':16A,19A '-74857':17A,20A 'api':4A 'auth':3A 'cve':15A,18A 'dsm':2A 'file':14A 'flaw':5A 'let':6A 'log':8A 'logged-in':7A 'read':11A 'synolog':1A 'user':10A 'write':13A","search_b":"'account':48B 'alreadi':45B 'also':62B 'api':39B 'arbitrari':53B 'attack':75B 'auth':38B 'authent':34B 'denial':72B 'denial-of-servic':71B 'devic':68B 'diskstat':29B 'dsm':21B 'file':54B 'flaw':60B 'host':26B 'infrastructur':22B 'knock':66B 'manag':30B 'miss':33B 'nas':23B,57B 'offlin':69B 'read':50B 'remot':42B 'self':25B 'self-host':24B 'servic':74B 'step':35B 'synolog':27B,28B 'use':64B 'user':43B 'write':52B","search_c":"'-1':99C '-5':95C '-86009':94C '-90080':98C '7.3.2':93C '7.4.1':97C 'allow':100C 'api':86C 'arbitrari':108C 'attack':116C 'auth':85C 'authent':81C,102C 'conduct':111C 'critic':78C 'denial':113C 'denial-of-servic':112C 'diskstat':89C 'dsm':91C 'file':109C 'manag':90C 'miss':77C 'read':105C 'remot':101C 'servic':115C 'step':79C 'synolog':88C 'user':103C 'vulner':82C 'write':107C","cause_entry":null,"cause_path":null,"disclosures_checked_at":null,"first_public_at":"2026-11-12T04:17:20+00:00","kev":null,"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvss_by":"security@synology.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-74857","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-74857","severity":null,"published_at":"2026-11-12T04:17:20+00:00","modified_at":"2026-11-12T04:17:20+00:00","first_seen_at":"2026-11-12T04:47:09+00:00","fetched_at":"2026-11-12T04:47:09+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"}