{"id":"CVE-2026-122129","kind":"vulnerability","aliases":["CVE-2026-122129"],"related":[],"title":"ipfixcol2: unbounded LZ4 buffer lets remote attackers exhaust collector memory","description":"CESNET ipfixcol2 2.7.1 before 2.9.0 contains a memory allocation vulnerability in Lz4Decoder::read_start_header() that allows unauthenticated attackers to exhaust memory by declaring unbounded ring buffer sizes. Attackers can open TCP connections sending LZ4 start headers with very large buffer sizes, forcing up to 4 GiB allocations per connection and denying collector service.","summary":"CESNET ipfixcol2 before 2.9.0 is an IPFIX flow collector whose LZ4 decoder trusts a declared ring buffer size from the start header. An unauthenticated attacker who opens TCP connections with very large sizes can force up to 4 GiB of allocation per connection and deny collector service.","severity":"medium","cvss":6.9,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ipfixcol2","linux","network-monitoring","other"],"not_affected_if":["file-input-only","firewalled-collector","no-tcp-listener"],"how_to_check":"- Check the installed ipfixcol2 version, for example with `ipfixcol2 --version` or the package manager, and see whether it is below `2.9.0`.\n- Look for an LZ4-compressed TCP IPFIX listener in the collector configuration.","fix":"- ipfixcol2: move to `2.9.0` or later","status":"open","published_at":"2026-11-04T21:18:08+00:00","first_seen_at":"2026-11-04T21:49:19+00:00","triaged_at":"2026-11-04T21:51:03+00:00","updated_at":"2026-11-04T21:51:03+00:00","category":"other","confidence":0.7,"triage":{"at":"2026-11-04T21:51:03Z","model":"claude-haiku-5-5","output":{"fix":"- ipfixcol2: move to `2.9.0` or later","reach":"network","title":"ipfixcol2: unbounded LZ4 buffer lets remote attackers exhaust collector memory","impact":"low","summary":"CESNET ipfixcol2 before 2.9.0 is an IPFIX flow collector whose LZ4 decoder trusts a declared ring buffer size from the start header. An unauthenticated attacker who opens TCP connections with very large sizes can force up to 4 GiB of allocation per connection and deny collector service.","audience":"businesses","category":"other","nicknames":[],"who_cares":["ipfixcol2","network-monitoring","linux"],"confidence":0.7,"fix_status":"available","needs_auth":"no","worst_case":"Remote attackers exhaust memory and stop the flow collector service.","analyst_note":"","how_to_check":"- Check the installed ipfixcol2 version, for example with `ipfixcol2 --version` or the package manager, and see whether it is below `2.9.0`.\n- Look for an LZ4-compressed TCP IPFIX listener in the collector configuration.","plain_action":"","needs_analyst":false,"not_affected_if":["file-input-only","no-tcp-listener","firewalled-collector"],"who_is_affected":"Teams running ipfixcol2 as a network flow collector that accepts TCP input with LZ4 compression can be hit remotely without credentials. Collectors that only read files, or that listen on UDP or are behind a firewall limiting who can connect, have less exposure. unknown whether a non-LZ4 configuration is affected.","user_interaction":"no","needs_special_setup":"yes","severity_if_unknown":"medium"},"cost_usd":0.00072,"input_tokens":4238,"output_tokens":593,"severity_before":"medium"},"analyst_status":null,"analyst_note":null,"search":"'-122129':13A,16A '-2026':12A,15A '2.7.1':71C '2.9.0':25B,73C '4':59B,114C 'alloc':62B,77C,116C 'allow':85C 'attack':7A,46B,87C,97C 'buffer':4A,38B,95C,109C 'cesnet':22B,69C 'collector':9A,30B,67B,121C 'connect':50B,64B,101C,118C 'contain':74C 'cve':11A,14A 'declar':36B,92C 'decod':33B 'deni':66B,120C 'exhaust':8A,89C 'flow':29B 'forc':56B,111C 'gib':60B,115C 'header':43B,83C,105C 'ipfix':28B 'ipfixcol2':1A,17B,23B,70C 'larg':53B,108C 'let':5A 'linux':18B 'lz4':3A,32B,103C 'lz4decoder':80C 'memori':10A,76C,90C 'monitor':21B 'network':20B 'network-monitor':19B 'open':48B,99C 'per':63B,117C 'read':81C 'remot':6A 'ring':37B,94C 'send':102C 'servic':68B,122C 'size':39B,54B,96C,110C 'start':42B,82C,104C 'tcp':49B,100C 'trust':34B 'unauthent':45B,86C 'unbound':2A,93C 'vulner':78C 'whose':31B","nicknames":[],"mitigations":[],"who_affected":"Teams running ipfixcol2 as a network flow collector that accepts TCP input with LZ4 compression can be hit remotely without credentials. Collectors that only read files, or that listen on UDP or are behind a firewall limiting who can connect, have less exposure. unknown whether a non-LZ4 configuration is affected.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["ipfixcol2","linux","medium","networkmonitoring","other"],"campaign_type":null,"first_public_at":"2026-11-04T21:18:08+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/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-2026-122129","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-122129","severity":null,"published_at":"2026-11-04T21:18:08+00:00","modified_at":"2026-11-04T21:18:08+00:00","first_seen_at":"2026-11-04T21:49:19+00:00","fetched_at":"2026-11-04T21:49:19+00:00","note":null}],"documents":[{"id":70645,"url":"https://github.com/CESNET/ipfixcol2/commit/1a199033eff847941353c5c039cb806a9ad8aa6f","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":70643,"url":"https://github.com/CESNET/ipfixcol2/releases/tag/v2.9.0","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":70647,"url":"https://www.vulncheck.com/advisories/cesnet-ipfixcol2-2.7.1-before-2.9.0-memory-exhaustion-via-tcp-lz4-decoder","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 at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}