# CVE-2026-121691: Unbounded decompression in the whatstk ZIP loader exhausts memory and disk


- **Severity:** Medium 6.7 (`CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 10 Nov 2026
- **Updated:** 10 Nov 2026
- **Also known as:** GHSA-q683-6fhr-jvg2

## What is CVE-2026-121691?

CVE-2026-121691 is a medium-severity vulnerability in lucasrodes whatstk, published on 10 Nov 2026. 

### Official description

Improper Handling of Highly Compressed Data (CWE-409) in the ZIP loader of whatstk from 0.7.0 before 0.9.0 allows a party that supplies a chat export to exhaust the memory and the disk of the process that parses it, because _str_from_file() (whatstk/whatsapp/parser.py) calls zip_ref.extractall() with no bound on the size of the members and no check of the compression ratio, then reads the extracted file in full with f.read(). The only guard on the archive counts the extracted files and raises when there is not exactly one, but it runs after extractall() has already written them, so it does not prevent the cost. _clean_text() then passes the whole text through unicodedata.normalize("NFKD", text), which holds a second copy, and the parse builds a list of regular expression matches and a DataFrame over it, so peak memory is a multiple of the decompressed text rather than of the archive. A ZIP is a documented input of WhatsAppChat.from_source() and df_from_whatsapp(), and is the form in which WhatsApp exports a chat on iOS, so the attacker supplies the whole file. This results in a small upload costing hundreds of megabytes of memory and of disk, and in the process being killed where that exceeds what is available.

Weakness: CWE-409 (Improper Handling of Highly Compressed Data (Data Amplification))

## Which versions are affected by CVE-2026-121691?


## How do I fix CVE-2026-121691?

No fix has been published for CVE-2026-121691 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-121691 being exploited?

There is no known exploitation of CVE-2026-121691 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-121691 and fix it if it is affected.

What it is: CVE-2026-121691 is a medium-severity vulnerability in lucasrodes whatstk, published on 10 Nov 2026. 
Exploitation: There is no known exploitation of CVE-2026-121691 in the wild and no public exploit code.

Affected product: lucasrodes whatstk. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-121691/ (Markdown: https://insights.sbomify.com/CVE-2026-121691/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-121691
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-121691
- OSV: https://osv.dev/vulnerability/CVE-2026-121691

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-121691/
Summaries are generated and may contain mistakes; the official description above is the record.