CVE-2025-66019Public exploitNetwork attack vector

Memory exhaustion via oversized LZWDecode output limit

Published Nov 25, 2025 · Updated Jan 20, 2026

Resource exhaustion in py-pdf pypdf before 6.4.0 allows remote attackers to consume up to 1 GB of memory per crafted LZWDecode stream. LzwCodec writes decoded bytes into an in-memory BytesIO buffer and permits output to grow to its 1,000,000,000-byte default limit. The host application must parse a page stream using the LZWDecode filter, causing memory pressure or service interruption without data disclosure or modification.

CVSS severityUnavailable
Unscored
EPSS probability0.36%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in py-pdf pypdf before 6.4.0 allows remote attackers to consume up to 1 GB of memory per crafted LZWDecode stream. LzwCodec writes decoded bytes into an in-memory BytesIO buffer and permits output to grow to its 1,000,000,000-byte default limit. The host application must parse a page stream using the LZWDecode filter, causing memory pressure or service interruption without data disclosure or modification.

The record

CVE
CVE-2025-66019
Published
Nov 25, 2025
Updated
Jan 20, 2026
Vendor
py-pdf
Product
pypdf
Classifications
CWE-409, CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 25, 2025CVE publishedPublication date reported by the CVE source.
  2. Jan 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 6.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

py-pdf · pypdfversion=< 6.4.0

Published CVSS scores

6.6GitHub, Inc.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

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-409Improper Handling of Highly Compressed Data (Data Amplification)
CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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