Unbounded decompression in the whatstk ZIP loader exhausts memory and disk
- Exploited
- No known exploitation
- Fix
- Fixed in 0.9.0
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.9.0.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 17/100 · provisional
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
The ZIP loader in the whatstk Python library lets a local attacker, without logging in, exhaust the memory and disk of the process that parses a chat export after a user loads a crafted ZIP file. A small archive can consume hundreds of megabytes of each, and the parsing process is killed once the available resources are exceeded.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
Read the original 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.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure?/25Unknown. No advisory context yet
- Reach10/20Affects PyPI packages
- Severity6.7/10CVSS 6.7
- No patch0/5No signal
What would change the score
- Would score about 72 if added to CISA KEV
- Would score about 67 if CISA's SSVC rates exploitation active
- Would score about 39 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 0.9.0.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-121691 (Unbounded decompression in the whatstk ZIP loader exhausts memory and disk), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-121691 (entry last updated 2026-11-10): Affected: - PyPI package whatstk: from 0.7.0, fixed in 0.9.0 Fixed versions: 0.9.0. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-121691 is not listed as of cve.now's last read. This KEV status is for CVE-2026-121691 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Packages (PyPI): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies. Verify against the linked advisories before concluding, and cite the date you read each one: - https://github.com/lucasrodes/whatstk/pull/182 - https://github.com/lucasrodes/whatstk/commit/01d66d8 - https://github.com/lucasrodes/whatstk/releases/tag/v0.9.0 - https://secur0.com/en/cna/cve-list/cve-2026-121691-whatstk-zip-decompression-bomb Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-121691 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-121691.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- whatstkPyPI
From 0.7.0 · fixed in 0.9.0
Evidence 6
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Corrections
None so far.
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Questions about CVE-2026-121691
Is CVE-2026-121691 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
Which versions are affected by CVE-2026-121691?
whatstk (PyPI): from 0.7.0 before 0.9.0.Source: cve.now feed data
How do I fix CVE-2026-121691?
Upgrade to a fixed version: 0.9.0.Source: cve.now feed data