# pypdf's LZWDecode streams be manipulated to exhaust RAM

Advisory record · `GHSA-m449-cwjh-6pw7`

- **Identifiers:** `GHSA-m449-cwjh-6pw7` · `CVE-2025-66019` · `PYSEC-2026-1832`
- **State:** Confirmed
- **Severity:** CVSS 6.6 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-400](https://cwe.mitre.org/data/definitions/400.html) · [CWE-409](https://cwe.mitre.org/data/definitions/409.html)
- **Tags:** [Denial of service](https://agentprime.io/advisories/tag/dos.md) · [CWE-409](https://agentprime.io/advisories/tag/cwe-409.md)
- **Published:** 24 Nov 2025
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 24 Nov 2025, 22:42 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `pypdf` (PyPI): affected `<6.4.0`; fixed in `6.4.0`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> The pypdf package before 6.4.0 can be made to use up to 1 GB of memory per stream when parsing a page's content stream that uses the LZWDecode filter. An attacker can do this by supplying a crafted PDF, which can exhaust RAM. Upgrade pypdf to 6.4.0 or later. The source gives a workaround that involves changing a default limit in code, but it is not described in detail here.

Written 5 Nov 2026.

## 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`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.0039, the 33rd percentile, on 6 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 31 Oct 2026, 14:34 UTC: First seen by agentprime
- 31 Oct 2026, 14:34 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-m449-cwjh-6pw7)

## Sources

- [GitHub Advisory Database: GHSA-m449-cwjh-6pw7](https://github.com/advisories/GHSA-m449-cwjh-6pw7)
- [OSV: GHSA-m449-cwjh-6pw7](https://osv.dev/vulnerability/GHSA-m449-cwjh-6pw7)
- <https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j>
- <https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7>
- <https://nvd.nist.gov/vuln/detail/CVE-2025-66019>
- <https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2>
- <https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dos>
- <https://github.com/py-pdf/pypdf>
- <https://github.com/py-pdf/pypdf/releases/tag/6.4.0>

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-m449-cwjh-6pw7>, 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-m449-cwjh-6pw7/>. Everything for agents: <https://agentprime.io/llms.txt>.