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VulnerabilityPublished Updated

CVE-2025-66019: py-pdf pypdf · Uncontrolled Resource Consumption

Affects py-pdf pypdfSource CVE Database V5

0

Not known to be exploited · CVSS 6.6 Medium : upgrade to 6.4.0 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 4.0 base score
6.6Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 29% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 6.4.0
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

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 25 Nov 2025

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade py-pdf pypdf to 6.4.0.

Affected software

ProductAffectedFixed in
PyPIpypdfpkg:pypi/pypdfOther threatsAffected
  • <6.4.0
Fixed in
  • 6.4.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

  1. Upgrade all instances of pypdf to version 6.4.0 or later immediately to incorporate the patch addressing this vulnerability.
  2. Implement strict input validation and sandboxing for PDF processing components to isolate and limit resource usage.
  3. Enforce memory and CPU usage limits on processes handling PDF parsing, using containerization or operating system-level controls.
  4. Monitor application logs and system metrics for unusual memory spikes or crashes related to PDF processing.
  5. Where feasible, restrict or sanitize PDFs from untrusted sources before processing.
  6. 7. Educate developers and system administrators about the risks of processing untrusted PDFs and the importance of timely updates.

Description

### 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 ```

References

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