{"id":"CVE-2026-121564","kind":"vulnerability","aliases":["CVE-2026-121564"],"related":[],"title":"whatstk: merge_chats() silently drops messages from merged WhatsApp chat exports","description":"Incomplete Comparison with Missing Factors (CWE-1023) in merge_chats() (whatstk/utils/chat_merge.py), reached from BaseChat.merge(), in whatstk from 0.3.0 before 0.9.0 allows a party that supplies the chat exports to cause messages to be absent from the merged output with no indication that anything was removed, because the merge keeps whole the chat whose first message is oldest and appends from the other only the messages that are strictly newer than the last message of the first. Every message of the second chat that falls inside the date range already covered by the first is therefore discarded. The two chats are compared on their date ranges and not on the identity of the individual messages, so a message held by only one of the two exports is dropped whenever its date falls inside the range of the other, and both branches of _merge_two_chats() behave this way. The merged result is returned without a warning and without a count of what was removed. This results in a merged chat that omits messages the inputs contain, in a library whose documented uses include forensic review and the generation of training data.","summary":"whatstk is a Python library for parsing WhatsApp chat exports. Its merge step silently discards messages from one export whenever their dates fall inside the date range of the other, so the merged chat omits content with no warning.","severity":"low","cvss":1.8,"epss":null,"exploited":false,"exploited_at":null,"products":[],"ecosystems":[],"tags":["forensics","package","python","training-data","whatstk"],"not_affected_if":["no-merge-calls","single-chat-parsing"],"how_to_check":"- Check the installed whatstk version with `pip show whatstk`; affected versions are from `0.3.0` before `0.9.0`.\n- Look for calls to `BaseChat.merge()` or `merge_chats()` in your code that combine overlapping chat exports.","fix":"- whatstk: move to `0.9.0` or later.","status":"open","published_at":"2026-11-03T16:17:29+00:00","first_seen_at":"2026-11-03T16:21:44+00:00","triaged_at":"2026-11-03T16:24:30+00:00","updated_at":"2026-11-03T16:24:30+00:00","category":"package","confidence":0.8,"triage":{"at":"2026-11-03T16:24:30Z","model":"claude-haiku-5-5","output":{"fix":"- whatstk: move to `0.9.0` or later.","reach":"local","title":"whatstk: merge_chats() silently drops messages from merged WhatsApp chat exports","impact":"low","summary":"whatstk is a Python library for parsing WhatsApp chat exports. Its merge step silently discards messages from one export whenever their dates fall inside the date range of the other, so the merged chat omits content with no warning.","audience":"developers","category":"package","nicknames":[],"who_cares":["python","whatstk","forensics","training-data"],"confidence":0.8,"fix_status":"available","needs_auth":"unknown","worst_case":"merged chat silently omits messages from the inputs","analyst_note":"","how_to_check":"- Check the installed whatstk version with `pip show whatstk`; affected versions are from `0.3.0` before `0.9.0`.\n- Look for calls to `BaseChat.merge()` or `merge_chats()` in your code that combine overlapping chat exports.","plain_action":"","needs_analyst":false,"not_affected_if":["single-chat-parsing","no-merge-calls"],"who_is_affected":"Teams that use whatstk to merge two or more WhatsApp chat exports with overlapping date ranges, for example in forensic review or when building training data. Code that parses a single export, or never calls merge, is not affected. The flaw only loses data during merging, so it does not give an attacker code execution.","user_interaction":"no","needs_special_setup":"no","severity_if_unknown":"low"},"cost_usd":0.000701,"input_tokens":4397,"output_tokens":523,"severity_before":"low"},"analyst_status":null,"analyst_note":null,"search":"'-1023':70C '-121564':14A,17A '-2026':13A,16A '0.3.0':81C '0.9.0':83C 'absent':97C 'allow':84C 'alreadi':152C 'anyth':106C 'append':122C 'basechat.merge':77C 'behav':208C 'branch':203C 'caus':93C 'chat':3A,10A,33B,58B,73C,90C,115C,145C,162C,207C,232C 'compar':164C 'comparison':65C 'contain':238C 'content':60B 'count':222C 'cover':153C 'cve':12A,15A 'cwe':69C 'data':23B,253C 'date':46B,50B,150C,167C,193C 'discard':39B,159C 'document':243C 'drop':5A,190C 'everi':140C 'export':11A,34B,43B,91C,188C 'factor':68C 'fall':47B,147C,194C 'first':117C,139C,156C 'forens':18B,246C 'generat':250C 'held':181C 'ident':173C 'includ':245C 'incomplet':64C 'indic':104C 'individu':176C 'input':237C 'insid':48B,148C,195C 'keep':112C 'last':135C 'librari':29B,241C 'merg':2A,8A,36B,57B,72C,100C,111C,205C,212C,231C 'messag':6A,40B,94C,118C,128C,136C,141C,177C,180C,235C 'miss':67C 'newer':132C 'oldest':120C 'omit':59B,234C 'one':42B,184C 'output':101C 'packag':19B 'pars':31B 'parti':86C 'python':20B,28B 'rang':51B,151C,168C,197C 'reach':75C 'remov':108C,226C 'result':213C,228C 'return':215C 'review':247C 'second':144C 'silent':4A,38B 'step':37B 'strict':131C 'suppli':88C 'therefor':158C 'train':22B,252C 'training-data':21B 'two':161C,187C,206C 'use':244C 'warn':63B,218C 'way':210C 'whatsapp':9A,32B 'whatstk':1A,24B,25B,79C 'whatstk/utils/chat_merge.py':74C 'whenev':44B,191C 'whole':113C 'whose':116C,242C 'without':216C,220C","nicknames":[],"mitigations":[],"who_affected":"Teams that use whatstk to merge two or more WhatsApp chat exports with overlapping date ranges, for example in forensic review or when building training data. Code that parses a single export, or never calls merge, is not affected. The flaw only loses data during merging, so it does not give an attacker code execution.","tier":"C","verified":{},"analyst_revisit_at":null,"fix_status":"available","audience":"developers","plain_action":null,"pkeys":[],"ptokens":[],"labels":["forensics","low","package","python","trainingdata","whatstk"],"campaign_type":null,"first_public_at":"2026-11-03T16:17:29+00:00","kev":null,"cvss_vector":"CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:N/VI:L/VA:N/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":"4daa8cea-433a-44bd-9456-53b127fc289a","poc_count":0,"sources":[{"source":"nvd","external_id":"CVE-2026-121564","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-121564","severity":null,"published_at":"2026-11-03T16:17:29+00:00","modified_at":"2026-11-03T16:17:29+00:00","first_seen_at":"2026-11-03T16:21:44+00:00","fetched_at":"2026-11-03T16:21:44+00:00","note":null}],"documents":[{"id":58866,"url":"https://github.com/lucasrodes/whatstk/commit/01d66d8","title":"Patch: github.com","kind":"other","source":"nvd","publisher":"vendor","text":null,"published_at":null,"relation":"fix","confidence":null,"note":"Patch: github.com"},{"id":58867,"url":"https://github.com/lucasrodes/whatstk/releases/tag/v0.9.0","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"}],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}