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Urllib3 CVE-2019-11236

MEDIUM
Improper Neutralization of CRLF Sequences ('CRLF Injection') (CWE-93)
2019-04-15 cve@mitre.org
6.1
CVSS 3.0 · NVD
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Vulnerability Assessment

Weakness
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization CRLF sequence sanitization
Impact

CVSS score of 6.1 (MEDIUM). Attack characteristics: network attack vector, low complexity, no privileges required, user interaction required. Public proof-of-concept exploit code is available.

Exploit ScenarioDerived

This vulnerability can be exploited remotely over the network. Successful exploitation could compromise the medium-severity affected system.

This Month Plan within 30 days. Why: MEDIUM severity (CVSS 4.0-6.9).
Patch available 2.1% exploitation probability (EPSS)

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AnalysisAI

In the urllib3 library through 1.24.1 for Python, CRLF injection is possible if the attacker controls the request parameter. Rated medium severity (CVSS 6.1), this vulnerability is remotely exploitable, no authentication required, low attack complexity. Public exploit code available and no vendor patch available.

RemediationAI

No vendor patch is available at time of analysis. Monitor vendor advisories for updates. Apply vendor patches when available. Implement network segmentation and monitoring as interim mitigations.

Affected Packages

pypi urllib3 fix: 1.24.3

Source: OSV (Open Source Vulnerabilities)

Affects your stack

Affects 1 package in pypi

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This vulnerability is classified under CWE-93. In the urllib3 library through 1.24.1 for Python, CRLF injection is possible if the attacker controls the request parameter. Affected products include: Python Urllib3. Version information: through 1.24.1.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

NVD PRIMARY 6.1 MEDIUM
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
None

DescriptionNVD

In the urllib3 library through 1.24.1 for Python, CRLF injection is possible if the attacker controls the request parameter.

Threat Intelligence Overview

EPSS Score
2.1%
Top 21% exploitable
Exploit
POC
Public exploit code exists
Data Quality
3 sources
Confidence: Low

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue
Severity MEDIUM
CISA KEV No
Public POC Yes
EPSS 2.1%
Patch available Yes
Active threat No
Deciding rule
MEDIUM severity (CVSS 4.0-6.9)
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived
Scheduled
Exploitation· derived
Poc
System Exposure· derived
Open
Automatable· derived
No
Human Impact· derived
Medium

Priority Score

52
Low Medium High Critical
KEV: 0
EPSS: +2
CVSS: +30
PoC: +20
Weaponized: 0
Threat intel: 0
Gov advisory: 0

Attack Technique

Code Injection CRITICAL

Code injection occurs when an application accepts user input and passes it directly into a language interpreter or evaluator without proper sanitization.

Affected Products (CPE)NVD

cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:*
CVE-2024-37891 MEDIUM POC
6.5 Jun 17

urllib3 is a user-friendly HTTP client library for Python. Rated medium severity (CVSS 6.5), this vulnerability is remot

CVE-2018-20060 CRITICAL
9.8 Dec 11

urllib3 before version 1.23 does not remove the Authorization HTTP header when following a cross-origin redirect (i.e.,

CVE-2025-50181 MEDIUM POC
5.3 Jun 19

urllib3 is a user-friendly HTTP client library for Python. Prior to 2.5.0, it is possible to disable redirects for all r

CVE-2026-97689 HIGH
8.9 Sep 29

Unbounded memory allocation in urllib3 (1.10.3 through 2.7.x) lets a malicious or machine-in-the-middle HTTP server exha

CVE-2025-66418 HIGH
8.9 Dec 05

Resource-exhaustion denial of service in urllib3 1.24 through 2.5.x allows a malicious or attacker-controlled HTTP serve

CVE-2025-66471 HIGH
8.9 Dec 05

A decompression-bomb denial-of-service flaw in the urllib3 Python HTTP client library (versions 1.0 through 2.5.x, fixed

CVE-2026-21441 HIGH
8.9 Jan 07

Uncontrolled resource consumption in the Python urllib3 HTTP client library (versions 1.22 through 2.6.2) lets a malicio

CVE-2023-43804 HIGH
8.1 Oct 04

urllib3 is a user-friendly HTTP client library for Python. Rated high severity (CVSS 8.1), this vulnerability is remotel

CVE-2026-97687 HIGH
7.6 Sep 29

Certificate validation bypass in urllib3 1.26.0 through 2.7.x allows a man-in-the-middle attacker who can impersonate th

CVE-2021-33503 HIGH
7.5 Jun 29

An issue was discovered in urllib3 before 1.26.5. Rated high severity (CVSS 7.5), this vulnerability is remotely exploit

CVE-2020-7212 HIGH
7.5 Mar 06

The _encode_invalid_chars function in util/url.py in the urllib3 library 1.25.2 through 1.25.7 for Python allows a denia

CVE-2019-11324 HIGH
7.5 Apr 18

The urllib3 library before 1.24.2 for Python mishandles certain cases where the desired set of CA certificates is differ

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