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Vulnerabilities

Vulnerability · CVE-2025-66418

urllib3 is a user-friendly HTTP client library for Python.

Published Dec 5, 2025 · catalog updated Dec 5, 2025 · urllib3 is a user-friendly

Last checked Oct 28, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2025-66418. EPSS is 0.68%. Act only if a listed version of urllib3 is a user-friendly is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (urllib3 is a user-friendly).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.

Same product and reporting

Severity
High8.9
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.68%
Remediation
Version ranges on file
Affected products
vendor urllib3 urllib3 1.24, < 2.6.0

urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor urllib3 urllib3 1.24, < 2.6.01.24, < 2.6.0

How to fix CVE-2025-66418

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2025-66418. EPSS is 0.68%. Act only if a listed version of urllib3 is a user-friendly is installed.

Which versions are affected?

Compare what you have installed with urllib3 urllib3 1.24, < 2.6.0 1.24, < 2.6.0. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.68%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Dec 5, 2025 · EUVD

    Detected

    urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

  2. Dec 5, 2025 · EUVD

    Updated

    urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage and massive memory allocation for the decompressed data. This vulnerability is fixed in 2.6.0.

Sources

  • CVE.orgVulnerability recordCVE-2025-66418

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2025-66418

    30-day exploitation probability 0.68%

    first.org
  • EUVDVulnerability recordEUVD-2025-201421

    urllib3 is a user-friendly HTTP client library for Python. Starting in version 1.24 and prior to 2.6.0, the number of links in the decompression chain was unbounded allowing a malicious server to insert a virtually unlimited number of compression steps leading to high CPU usage a

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Oct 28, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSOct 28, 2026
  • CVE.orgOct 28, 2026
  • EUVDOct 27, 2026