{"id":"CVE-2026-123271","kind":"vulnerability","aliases":["CVE-2026-123271"],"related":[],"title":"ChatCLI: MCP OAuth login can leak bearer tokens to other resources","description":"ChatCLI before v1.215.2 contains an improper validation vulnerability in the MCP OAuth login flow that uses server-supplied Protected Resource Metadata as the resource indicator without checking it matches the configured server URL. A malicious MCP server can declare another resource on the same authorization server, obtain the user's bearer token for it, and replay that token against the other resource.","summary":"ChatCLI before v1.215.2 trusts the resource URL that a remote MCP server supplies during its OAuth login flow without checking it against the configured server. A malicious MCP server can get a user's bearer token issued for another resource and then replay that token against it.","severity":"high","cvss":8.0,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ai-tooling","chatcli","developers","mcp","oauth"],"not_affected_if":["no-mcp-oauth","no-untrusted-mcp-servers"],"how_to_check":"- Check the installed ChatCLI version and confirm whether it is below `v1.215.2`.\n- Look for MCP servers configured in ChatCLI that use OAuth login.","fix":"- ChatCLI: move to `v1.215.2` or later.","status":"open","published_at":"2026-11-05T19:17:20+00:00","first_seen_at":"2026-11-05T19:40:36+00:00","triaged_at":"2026-11-05T19:42:56+00:00","updated_at":"2026-11-05T19:42:56+00:00","category":"ai-tooling","confidence":0.6,"triage":{"at":"2026-11-05T19:42:56Z","model":"claude-haiku-5-5","output":{"fix":"- ChatCLI: move to `v1.215.2` or later.","reach":"network","title":"ChatCLI: MCP OAuth login can leak bearer tokens to other resources","impact":"high","summary":"ChatCLI before v1.215.2 trusts the resource URL that a remote MCP server supplies during its OAuth login flow without checking it against the configured server. A malicious MCP server can get a user's bearer token issued for another resource and then replay that token against it.","audience":"developers","category":"ai-tooling","nicknames":[],"who_cares":["chatcli","mcp","oauth","developers"],"confidence":0.6,"fix_status":"available","needs_auth":"unknown","worst_case":"attacker obtains user's bearer token for another resource","analyst_note":"Confirm the fixed version and any exposure checks at the NVD entry and the vendor advisory linked from the sources.","how_to_check":"- Check the installed ChatCLI version and confirm whether it is below `v1.215.2`.\n- Look for MCP servers configured in ChatCLI that use OAuth login.\n- unknown whether other check steps are needed; the sources do not say.","plain_action":"","needs_analyst":true,"not_affected_if":["no-mcp-oauth","no-untrusted-mcp-servers"],"who_is_affected":"Teams that run ChatCLI and connect it to MCP servers that use OAuth login are exposed, since a malicious or compromised MCP server could collect a token. Installations that do not use MCP OAuth login are not affected by this flaw, as described in the sources.","user_interaction":"yes","needs_special_setup":"yes","severity_if_unknown":"high"},"cost_usd":0.00072,"input_tokens":4317,"output_tokens":577,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-123271':14A,17A '-2026':13A,16A 'ai':19B 'ai-tool':18B 'anoth':63B,110C 'author':115C 'bearer':7A,59B,121C 'chatc':1A,21B,25B,70C 'check':44B,97C 'configur':48B,101C 'contain':73C 'cve':12A,15A 'declar':109C 'develop':22B 'flow':42B,83C 'get':55B 'improp':75C 'indic':95C 'issu':61B 'leak':6A 'login':4A,41B,82C 'malici':51B,105C 'match':99C 'mcp':2A,23B,35B,52B,80C,106C 'metadata':91C 'oauth':3A,24B,40B,81C 'obtain':117C 'protect':89C 'remot':34B 'replay':67B,126C 'resourc':11A,30B,64B,90C,94C,111C,132C 'server':36B,49B,53B,87C,102C,107C,116C 'server-suppli':86C 'suppli':37B,88C 'token':8A,60B,69B,122C,128C 'tool':20B 'trust':28B 'url':31B,103C 'use':85C 'user':57B,119C 'v1.215.2':27B,72C 'valid':76C 'vulner':77C 'without':43B,96C","nicknames":[],"mitigations":[],"who_affected":"Teams that run ChatCLI and connect it to MCP servers that use OAuth login are exposed, since a malicious or compromised MCP server could collect a token. Installations that do not use MCP OAuth login are not affected by this flaw, as described in the sources.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["aitooling","chatcli","developers","high","mcp","oauth"],"campaign_type":null,"first_public_at":"2026-10-11T04:12:25+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:N/VI:N/VA:N/SC:H/SI:H/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":"disclosure@vulncheck.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-123271","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-123271","severity":null,"published_at":"2026-11-05T19:17:20+00:00","modified_at":"2026-11-05T19:17:20+00:00","first_seen_at":"2026-11-05T19:40:36+00:00","fetched_at":"2026-11-05T19:40:36+00:00","note":null}],"documents":[{"id":79215,"url":"https://github.com/diillson/chatcli/commit/951fe24b8e090eae86bf8edb13a788916b1e6c91","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":79216,"url":"https://github.com/diillson/chatcli/releases/tag/v1.215.2","title":"Release notes: github.com","kind":"release","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Release notes: github.com"},{"id":79217,"url":"https://github.com/diillson/chatcli/security/advisories/GHSA-95vg-3r9c-2v5q","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-10-11T04:12:25+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"},{"id":79218,"url":"https://www.vulncheck.com/advisories/chatcli-before-1.215.2-origin-validation-error-via-unvalidated-mcp-oauth-resource-indicator","title":"Third-party advisory: www.vulncheck.com","kind":"advisory","source":"nvd","publisher":"research","text":null,"published_at":null,"relation":"advisory","confidence":null,"note":"Third-party advisory: www.vulncheck.com"}],"exploit_sources":[],"notice":"Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai"}