---
id: "CVE-2026-121564"
kind: "vulnerability"
aliases: ["CVE-2026-121564"]
title: "whatstk: merge_chats() silently drops messages from merged WhatsApp chat exports"
severity: "low"
cvss: 1.8
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["forensics", "package", "python", "training-data", "whatstk"]
not_affected_if: ["no-merge-calls", "single-chat-parsing"]
published_at: "2026-11-03T16:17:29+00:00"
first_seen_at: "2026-11-03T16:21:44+00:00"
updated_at: "2026-11-03T16:24:30+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-121564", "first_seen_at": "2026-11-03T16:21:44+00:00"}]
---

# whatstk: merge_chats() silently drops messages from merged WhatsApp chat exports

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.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the installed whatstk version with `pip show whatstk`; affected versions are from `0.3.0` before `0.9.0`.
- 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.

## Timeline

- 2026-11-03T16:21:44+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-121564

## Documents

- [fix] Patch: github.com https://github.com/lucasrodes/whatstk/commit/01d66d8
- [fix] Release notes: github.com https://github.com/lucasrodes/whatstk/releases/tag/v0.9.0

## From the sources

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.

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