{"id":"CVE-2026-121520","kind":"vulnerability","aliases":["CVE-2026-121520"],"related":[],"title":"BuildKit: build requests can set extended attributes outside the state directory","description":"In BuildKit versions prior to v0.34.1, a malicious client with access to the BuildKit control APIs can submit a build request that sets an extended attribute on a file outside the BuildKit state directory. Extended attributes in the trusted. or security. namespaces may also be set, potentially giving a program on the host elevated privileges. This issue affects build services that accept build requests from untrusted users. The issue is fixed in v0.34.1.","summary":"A malicious client with access to BuildKit's control APIs can submit a build request that sets an extended attribute on a file outside the BuildKit state directory. Attributes in the trusted. or security. namespaces can also be set, which may give a host program elevated privileges.","severity":"medium","cvss":4.5,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["buildkit","ci","docker","infrastructure","kubernetes"],"not_affected_if":["trusted-clients-only"],"how_to_check":"- Check the BuildKit version with `buildkitd --version` or `buildctl --version`\n- Check whether build services accept build requests from untrusted users","fix":"- BuildKit: move to `v0.34.1` or later","status":"open","published_at":"2026-11-03T23:17:34+00:00","first_seen_at":"2026-11-03T23:45:14+00:00","triaged_at":"2026-11-03T23:45:50+00:00","updated_at":"2026-11-03T23:45:50+00:00","category":"infrastructure","confidence":0.6,"triage":{"at":"2026-11-03T23:45:50Z","model":"claude-haiku-5-5","output":{"fix":"- BuildKit: move to `v0.34.1` or later","reach":"network","title":"BuildKit: build requests can set extended attributes outside the state directory","impact":"medium","summary":"A malicious client with access to BuildKit's control APIs can submit a build request that sets an extended attribute on a file outside the BuildKit state directory. Attributes in the trusted. or security. namespaces can also be set, which may give a host program elevated privileges.","audience":"businesses","category":"infrastructure","nicknames":[],"who_cares":["buildkit","docker","ci","kubernetes"],"confidence":0.6,"fix_status":"available","needs_auth":"yes","worst_case":"host file extended attributes set, possibly elevating a host program","analyst_note":"","how_to_check":"- Check the BuildKit version with `buildkitd --version` or `buildctl --version`\n- Check whether build services accept build requests from untrusted users","plain_action":"","needs_analyst":false,"not_affected_if":["trusted-clients-only"],"who_is_affected":"Only build services that accept build requests from untrusted users are described as exposed. A BuildKit deployment that only takes requests from trusted users is not described as exposed by the sources. unknown for anything beyond that.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"medium"},"cost_usd":0.000653,"input_tokens":4186,"output_tokens":468,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-121520':14A,17A '-2026':13A,16A 'accept':131C 'access':27B,80C 'affect':127C 'also':59B,113C 'api':32B,85C 'attribut':7A,42B,51B,95C,105C 'build':2A,36B,89C,128C,132C 'buildkit':1A,18B,29B,48B,71C,83C,101C 'ci':19B 'client':25B,78C 'control':31B,84C 'cve':12A,15A 'directori':11A,50B,103C 'docker':20B 'elev':68B,123C 'extend':6A,41B,94C,104C 'file':45B,98C 'fix':140C 'give':64B,117C 'host':66B,122C 'infrastructur':21B 'issu':126C,138C 'kubernet':22B 'malici':24B,77C 'may':63B,112C 'namespac':57B,111C 'outsid':8A,46B,99C 'potenti':116C 'prior':73C 'privileg':69B,124C 'program':67B,119C 'request':3A,37B,90C,133C 'secur':56B,110C 'servic':129C 'set':5A,39B,61B,92C,115C 'state':10A,49B,102C 'submit':34B,87C 'trust':54B,108C 'untrust':135C 'user':136C 'v0.34.1':75C,142C 'version':72C","nicknames":[],"mitigations":[],"who_affected":"Only build services that accept build requests from untrusted users are described as exposed. A BuildKit deployment that only takes requests from trusted users is not described as exposed by the sources. unknown for anything beyond that.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["buildkit","ci","docker","infrastructure","kubernetes","medium"],"campaign_type":null,"first_public_at":"2026-11-03T19:25:18+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:H/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@docker.com","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-121520","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121520","severity":null,"published_at":"2026-11-03T23:17:34+00:00","modified_at":"2026-11-03T23:17:34+00:00","first_seen_at":"2026-11-03T23:45:14+00:00","fetched_at":"2026-11-03T23:45:14+00:00","note":null}],"documents":[{"id":61620,"url":"https://github.com/moby/buildkit/security/advisories/GHSA-w26x-xg27-7qjc","title":"Vendor advisory: github.com","kind":"vendor","source":"nvd","publisher":"vendor","text":null,"published_at":"2026-11-03T19:25:18+00:00","relation":"advisory","confidence":null,"note":"Vendor advisory: github.com"}],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}