CVE-2020-7212 Uncontrolled Resource Consumption in urllib3
An attacker can cause a denial of service via CPU exhaustion in urllib3 by submitting URLs with many percent-encoded characters, triggering quadratic time complexity.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2020-7212?
CVE-2020-7212 is a high-severity denial of service vulnerability in n/a, published on 6 Mar 2020. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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).
Weakness: CWE-400
Which versions are affected by CVE-2020-7212?
3 open source packages ship an affected version, including urllib3. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
urllib3 PyPI | From 1.25.2 | 1.25.8 |
urllib3 PyPI | From 1.25.2 | 1.25.8 |
urllib3 PyPI | From 1.25.2 | 1.25.8 |
Products include Python Urllib3.
How do I fix CVE-2020-7212?
Upgrade urllib3 to 1.25.8 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2020-7212 being exploited?
There is no known exploitation of CVE-2020-7212 in the wild and no public exploit code.
Other vulnerabilities in n/a
- CVE-2026-97689 urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory
- CVE-2026-44432 urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API
- CVE-2026-21441 urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (streaming API)
- CVE-2025-66418 urllib3 allows an unbounded number of links in the decompression chain
- CVE-2025-66471 urllib3 Streaming API improperly handles highly compressed data
Sources
Also known as DEBIAN-CVE-2020-7212, GHSA-hmv2-79q8-fv6g, PYSEC-2020-149, ROOT-APP-PYPI-CVE-2020-7212.