# 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.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 6 Mar 2020
- **Updated:** 4 Aug 2024
- **Also known as:** DEBIAN-CVE-2020-7212, GHSA-hmv2-79q8-fv6g, PYSEC-2020-149, ROOT-APP-PYPI-CVE-2020-7212

## 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 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2020-7212?

3 open source packages ship an affected version, including urllib3. It affects 1 product.


| Package | Ecosystem | 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: Python Urllib3.

## How do I fix CVE-2020-7212?

Upgrade urllib3 to 1.25.8 or later.

## 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](https://insights.sbomify.com/CVE-2026-97689/): urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory (high 8.9)
- [CVE-2026-44432](https://insights.sbomify.com/CVE-2026-44432/): urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API (high 8.9)
- [CVE-2026-21441](https://insights.sbomify.com/CVE-2026-21441/): urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (streaming API) (high 8.9)
- [CVE-2025-66418](https://insights.sbomify.com/CVE-2025-66418/): urllib3 allows an unbounded number of links in the decompression chain (high 8.9)
- [CVE-2025-66471](https://insights.sbomify.com/CVE-2025-66471/): urllib3 Streaming API improperly handles highly compressed data (high 8.9)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-7212 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2020-7212 in the wild and no public exploit code.

Affected packages and fixed versions:
- urllib3 (PyPI): affected from 1.25.2; fixed in 1.25.8
- urllib3 (PyPI): affected from 1.25.2; fixed in 1.25.8
- urllib3 (PyPI): affected from 1.25.2; fixed in 1.25.8

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-7212/ (Markdown: https://insights.sbomify.com/CVE-2020-7212/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-7212
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-7212
- OSV: https://osv.dev/vulnerability/CVE-2020-7212

---
From sbomify Insights: https://insights.sbomify.com/CVE-2020-7212/
Summaries are generated and may contain mistakes; the official description above is the record.