CVE-2020-7212
The _encode_invalid_chars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denial of service (CPU consumption) because of an inefficient algorithm.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (3.37%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
Description
The _encode_invalid_chars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denial of service (CPU consumption) because of an inefficient algorithm. The percent_encodings array contains all matches of percent encodings. It is not deduplicated. For a URL of length N, the size of percent_encodings may be up to O(N). The next step (normalize existing percent-encoded bytes) also takes up to O(N) for each step, so the total time is O(N^2). If percent_encodings were deduplicated, the time to compute _encode_invalid_chars would be O(kN), where k is at most 484 ((10+6*2)^2).
- CVSS 3.1
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 3.37% probability · 88th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-400
- Affected
- python/urllib3
- Source
- cve@mitre.org
References
- https://github.com/urllib3/urllib3/blob/master/CHANGES.rstRelease Notes, Third Party Advisory
- https://github.com/urllib3/urllib3/commit/a74c9cfbaed9f811e7563cfc3dce894928e0221aPatch, Third Party Advisory
- https://pypi.org/project/urllib3/1.25.8/Release Notes, Vendor Advisory
- https://github.com/urllib3/urllib3/blob/master/CHANGES.rstRelease Notes, Third Party Advisory
- https://github.com/urllib3/urllib3/commit/a74c9cfbaed9f811e7563cfc3dce894928e0221aPatch, Third Party Advisory
- https://pypi.org/project/urllib3/1.25.8/Release Notes, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.