Vulnerability Intelligence Report
urllib3 allows an unbounded number of links in the decompression chain
CVE-2025-66418
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.
No Active Exploit Signals
CVSS Base Score
8.9
HIGH
EPSS Probability:0.62%
Executive Threat Verdict
Evaluating...
Evaluating Threat Landscape...
Assessing known weaponization, exploitation telemetry, and federal advisories.
Attack Surface
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Authentication
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Weaponization
—
SSVC Action
—
Weaknesses (CWE)
CWE-770 ↗CWE-770: Allocation of Resources Without Limits or Throttling
Affected Products & Versions
| Vendor | Product | Affected Versions |
|---|---|---|
| urllib3 | urllib3 | >= 1.24, < 2.6.0 (affected) |
References & Technical Advisories
No reference links found.
Threat Intelligence Signals
EPSS Score
0.622%
GitHub Advisory
Identity & Timeline
| Status | PUBLISHED |
| Assigning Authority | GitHub, Inc. · Vendor · USA |
| Reserved | 2025-11-28T23:33:56 |
| Published | 2025-12-05T16:02:15 |
| Last Updated | 2025-12-05T18:15:28 |
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