pypdf's LZWDecode streams be manipulated to exhaust RAM
### Impact An attacker who uses this vulnerability can craft a PDF which leads to a memory usage of up to 1 GB per stream. This requires parsing the content stream of a page using the LZWDecode filter. This is a follow up to [GHSA-jfx9-29x2-rv3j](https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3j) to align the default limit with the one for *zlib*. ### Patches This has been fixed in [pypdf==6.4.0](https://github.com/py-pdf/pypdf/releases/tag/6.4.0). ### Workarounds If users cannot upgrade yet, use the line below to overwrite the default in their code: ```python pypdf.filters.LZW_MAX_OUTPUT_LENGTH = 75_000_000 ```
describes (1)
Related CVEs.
| ID | severity | exploitable | ||
|---|---|---|---|---|
| CVE-2025-66019US | — | — | ||
pypdf is a free and open-source pure-python PDF library. Prior to version 6.4.0, an attacker who uses this vulnerability can craft a PDF which leads to a memory usage of up to 1 GB… | ||||
references
External citations — patches, advisories, analysis.
- https://aydinnyunus.github.io/2025/12/20/cve-2025-66019-pypdf-lzw-dosWEB
- https://github.com/advisories/GHSA-m449-cwjh-6pw7ADVISORY
- https://github.com/py-pdf/pypdfPACKAGE
- https://github.com/py-pdf/pypdf/commit/96186725e5e6f237129a58a97cd19204a9ce40b2WEB
- https://github.com/py-pdf/pypdf/releases/tag/6.4.0WEB
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-jfx9-29x2-rv3jWEB
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-m449-cwjh-6pw7WEB
- https://nvd.nist.gov/vuln/detail/CVE-2025-66019ADVISORY
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