{"id":"CVE-2026-122127","kind":"vulnerability","aliases":["CVE-2026-122127"],"related":[],"title":"ipfixcol2: LZ4 decoder heap overflow lets network peers crash the collector","description":"CESNET ipfixcol2 2.7.1 before 2.9.0 contains a heap-based buffer overflow in Lz4Decoder.cpp that allows unauthenticated network peers to write past heap buffers. Attackers can declare a small ring buffer_size followed by a large decompressed_size to write up to 65535 controlled bytes and crash the collector.","summary":"ipfixcol2 is a flow-data collector whose LZ4 decoder writes past a heap buffer when a crafted packet declares a small ring buffer size and a large decompressed size. An unauthenticated network peer can write up to 65535 controlled bytes and crash the collector.","severity":"high","cvss":8.7,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["ipfixcol2","netflow-collectors","package","self-hosted"],"not_affected_if":["no-network-listener","version-2.9.0-or-later"],"how_to_check":"- Check the installed ipfixcol2 version with `ipfixcol2 --version` or the package manager, and see whether it is below `2.9.0`\n- Confirm whether the collector accepts LZ4-compressed IPFIX input from the network","fix":"- ipfixcol2 `2.9.0` (fixed version; sources state versions before 2.9.0 are affected)","status":"open","published_at":"2026-11-04T21:18:08+00:00","first_seen_at":"2026-11-04T21:49:19+00:00","triaged_at":"2026-11-04T21:50:39+00:00","updated_at":"2026-11-04T21:50:39+00:00","category":"package","confidence":0.7,"triage":{"at":"2026-11-04T21:50:39Z","model":"claude-haiku-5-5","output":{"fix":"- ipfixcol2 `2.9.0` (fixed version; sources state versions before 2.9.0 are affected)","reach":"network","title":"ipfixcol2: LZ4 decoder heap overflow lets network peers crash the collector","impact":"medium","summary":"ipfixcol2 is a flow-data collector whose LZ4 decoder writes past a heap buffer when a crafted packet declares a small ring buffer size and a large decompressed size. An unauthenticated network peer can write up to 65535 controlled bytes and crash the collector.","audience":"businesses","category":"package","nicknames":[],"who_cares":["ipfixcol2","netflow-collectors","self-hosted"],"confidence":0.7,"fix_status":"available","needs_auth":"no","worst_case":"Unauthenticated peer crashes the collector and may write controlled heap bytes","analyst_note":"","how_to_check":"- Check the installed ipfixcol2 version with `ipfixcol2 --version` or the package manager, and see whether it is below `2.9.0`\n- Confirm whether the collector accepts LZ4-compressed IPFIX input from the network","plain_action":"","needs_analyst":false,"not_affected_if":["version-2.9.0-or-later","no-network-listener"],"who_is_affected":"Teams that run the ipfixcol2 collector (version 2.7.1 up to but not including 2.9.0) to receive IPFIX flow records over the network. Exposure depends on whether the collector accepts LZ4-compressed input from peers that can reach it; collectors on isolated networks with no reachable listener are lower risk. unknown whether other ipfixcol2 versions outside that range are affected.","user_interaction":"no","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000731,"input_tokens":4212,"output_tokens":619,"severity_before":"high"},"analyst_status":null,"analyst_note":null,"search":"'-122127':14A,17A '-2026':13A,16A '2.7.1':73C '2.9.0':75C '65535':64B,113C 'allow':86C 'attack':95C 'base':80C 'buffer':40B,49B,81C,94C,101C 'byte':66B,115C 'cesnet':71C 'collector':11A,21B,32B,70B,119C 'contain':76C 'control':65B,114C 'craft':43B 'crash':9A,68B,117C 'cve':12A,15A 'data':31B 'declar':45B,97C 'decod':3A,35B 'decompress':54B,107C 'flow':30B 'flow-data':29B 'follow':103C 'heap':4A,39B,79C,93C 'heap-bas':78C 'host':25B 'ipfixcol2':1A,18B,26B,72C 'larg':53B,106C 'let':6A 'lz4':2A,34B 'lz4decoder.cpp':84C 'netflow':20B 'netflow-collector':19B 'network':7A,58B,88C 'overflow':5A,82C 'packag':22B 'packet':44B 'past':37B,92C 'peer':8A,59B,89C 'ring':48B,100C 'self':24B 'self-host':23B 'size':50B,55B,102C,108C 'small':47B,99C 'unauthent':57B,87C 'whose':33B 'write':36B,61B,91C,110C","nicknames":[],"mitigations":[],"who_affected":"Teams that run the ipfixcol2 collector (version 2.7.1 up to but not including 2.9.0) to receive IPFIX flow records over the network. Exposure depends on whether the collector accepts LZ4-compressed input from peers that can reach it; collectors on isolated networks with no reachable listener are lower risk. unknown whether other ipfixcol2 versions outside that range are affected.","tier":"B","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"businesses","plain_action":null,"pkeys":[],"ptokens":[],"labels":["high","ipfixcol2","netflowcollectors","package","selfhosted"],"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:H/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-2026-122127","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-122127","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":70642,"url":"https://github.com/CESNET/ipfixcol2/commit/fd5cb168efb4b864d33f655174711b2779cef502","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":70644,"url":"https://www.vulncheck.com/advisories/cesnet-ipfixcol2-2.7.1-before-2.9.0-heap-buffer-overflow-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"}