{"id":"CVE-2026-42897","kind":"vulnerability","aliases":["CVE-2026-42897"],"related":[],"title":"Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Exchange Server…","description":"Microsoft Exchange Server contains a cross-site scripting vulnerability during web page generation in Outlook Web Access and when certain interaction conditions are met, arbitrary JavaScript can be executed in the browser context.\n\nCISA required action: Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","summary":"Microsoft Exchange Server has a cross-site scripting flaw in Outlook Web Access: when certain interaction conditions are met, an attacker can get arbitrary JavaScript to run in a user's browser session. CISA lists it as actively exploited.","severity":"high","cvss":8.1,"epss":null,"exploited":true,"exploited_at":"2026-05-15T00:00:00+00:00","products":[{"name":"Microsoft Microsoft","fixed":[],"affected":"","ecosystem":"vendor"},{"name":"microsoft exchange server","fixed":[],"affected":"= 2016","ecosystem":"vendor"},{"name":"microsoft exchange server","fixed":[],"affected":"= 2019","ecosystem":"vendor"},{"name":"microsoft exchange server subscription edition","fixed":["15.02.2562.043"],"affected":"< 15.02.2562.043","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exchange-server","exploited","on-premises-exchange","outlook-web-access","vendor"],"not_affected_if":["exchange-online"],"how_to_check":null,"fix":"Apply the mitigations in Microsoft's vendor advisory for CVE-2026-42897; the sources do not name the patched build. If no mitigation is available, CISA says to discontinue use of the product.","status":"open","published_at":"2026-05-14T18:16:49+00:00","first_seen_at":"2026-10-23T19:11:51+00:00","triaged_at":"2026-10-23T20:35:39+00:00","updated_at":"2026-10-23T23:44:51+00:00","category":"vendor","confidence":0.6,"triage":{"at":"2026-10-23T20:35:39Z","model":"claude-haiku-5-5","output":{"fix":"Apply the mitigations in Microsoft's vendor advisory for CVE-2026-42897; the sources do not name the patched build. If no mitigation is available, CISA says to discontinue use of the product.","summary":"Microsoft Exchange Server has a cross-site scripting flaw in Outlook Web Access: when certain interaction conditions are met, an attacker can get arbitrary JavaScript to run in a user's browser session. CISA lists it as actively exploited.","category":"vendor","who_cares":["exchange-server","outlook-web-access","on-premises-exchange"],"confidence":0.6,"analyst_note":"Find Microsoft's security update guide entry for CVE-2026-42897 for affected build numbers, the patch or mitigation steps, and the exploitation details; the KEV page only links to CISA search.","how_to_check":"unknown","needs_analyst":true,"not_affected_if":["exchange-online"],"severity_if_unknown":"high"},"cost_usd":0.000376,"input_tokens":2091,"output_tokens":333,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-01':135C '-2026':18A,21A '-42897':19A,22A '22':134C 'access':47B,62B,106C 'action':125C 'activ':87B 'appli':126C 'applic':132C 'arbitrari':73B,114C 'attack':70B 'bod':133C 'browser':81B,121C 'certain':64B,109C 'cisa':83B,123C 'cloud':138C 'condit':66B,111C 'contain':92C 'context':122C 'cross':10A,55B,95C 'cross-sit':9A,54B,94C 'cve':17A,20A 'discontinu':141C 'edition':35A 'exchang':15A,37B,43B,50B,90C 'exchange':26A,29A,32A 'exchange-serv':36B 'execut':118C 'exploit':39B,88B 'flaw':58B 'follow':131C 'generat':8A,102C 'get':72B 'guidanc':136C 'improp':1A 'input':4A 'instruct':130C 'interact':65B,110C 'javascript':74B,115C 'list':84B 'met':68B,113C 'microsoft':14A,23A,24A,25A,28A,31A,49B,89C 'mitig':127C,147C 'neutral':2A 'on-premises-exchang':40B 'outlook':45B,60B,104C 'outlook-web-access':44B 'page':7A,101C 'per':128C 'premis':42B 'product':145C 'requir':124C 'run':76B 'script':12A,57B,97C 'server':16A,27A,30A,33A,38B,51B,91C 'servic':139C 'session':82B 'site':11A,56B,96C 'subscription':34A 'unavail':149C 'use':142C 'user':79B 'vendor':48B,129C 'vulner':98C 'web':6A,46B,61B,100C,105C","nicknames":[],"mitigations":[],"who_affected":null,"tier":null,"verified":{},"analyst_revisit_at":null,"first_public_at":"2026-05-14T18:16:49+00:00","kev":{"dateAdded":"2026-05-15","dueDate":"2026-05-29","requiredAction":"Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N","cvss_by":"secure@microsoft.com","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2026-42897","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-42897","severity":null,"published_at":"2026-05-15T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-23T19:11:51+00:00","fetched_at":"2026-10-25T11:39:14+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-42897","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-42897","severity":null,"published_at":"2026-05-14T18:16:49+00:00","modified_at":"2026-06-17T10:48:34+00:00","first_seen_at":"2026-10-23T23:44:51+00:00","fetched_at":"2026-10-23T23:44:51+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"}