# fflate unzipSync can enter an infinite loop when parsing malformed ZIP64 archives

Advisory record · `GHSA-px8p-9vwx-vf98`

- **Identifiers:** `GHSA-px8p-9vwx-vf98` · `CVE-2026-45820`
- **State:** Confirmed
- **Severity:** CVSS 6.6 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-835](https://cwe.mitre.org/data/definitions/835.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md)
- **Published:** 22 Jul 2026
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 22 Jul 2026, 09:32 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `fflate` (npm): affected `>=0.4.5, <0.4.9 || >=0.5.0, <0.5.4 || >=0.6.0, <0.6.11 || >=0.7.0, <0.7.5 || >=0.8.0, <0.8.3`; fixed in `0.4.9`, `0.5.4`, `0.6.11`, `0.7.5`, `0.8.3`

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.6 Medium, CVSS 4.0: `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:U/S:N/AU:Y/R:U/V:D/RE:M/U:Amber`, from CNA (seal)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0028, the 20th percentile, on 15 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

This record came from the full history of the GitHub Advisory Database, published 22 Jul 2026. New records show when each source confirmed them.

## Sources

- [GitHub Advisory Database: GHSA-px8p-9vwx-vf98](https://github.com/advisories/GHSA-px8p-9vwx-vf98)
- [OSV: GHSA-px8p-9vwx-vf98](https://osv.dev/vulnerability/GHSA-px8p-9vwx-vf98)
- <https://nvd.nist.gov/vuln/detail/CVE-2026-45820>
- <https://github.com/101arrowz/fflate/commit/e6d5e6e1076892f72770ac732d83c81da9f3316e>
- <https://github.com/101arrowz/fflate>
- <https://github.com/101arrowz/fflate/blob/f7873560ad229c22c4b23b06c6a3806ffde77569/src/index.ts#L2714>
- <https://github.com/101arrowz/fflate/releases/tag/v0.8.3>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-px8p-9vwx-vf98>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-px8p-9vwx-vf98/>. Everything for agents: <https://agentprime.io/llms.txt>.