CVE-2020-7695: Uvicorn HTTP Response Splitting Vulnerability

HIGH
Advisory Identifier: GHSA-f97h-2pfx-f59f
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CVSS 7.5
CWE-74
Published
Advisory Summary

CVE-2020-7695 is a HIGH (CVSS 7.5) http response splitting vulnerability (CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')) affecting Uvicorn libraries in the PyPI ecosystem. The issue involves http response splitting in uvicorn. Remediation is available by upgrading affected packages to version 0.11.7.

CVE-2020-7695 at a Glance

CVE Identifier CVE-2020-7695
GHSA Identifier GHSA-f97h-2pfx-f59f
Severity HIGH
CVSS v3.1 Base Score 7.5
CWE Classification CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
Affected Product Uvicorn
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 7.5

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity High (I:H)
Availability None (A:N)

How to Fix CVE-2020-7695

To remediate this vulnerability, upgrade all affected Uvicorn dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

uvicorn fixed: 0.11.7 
pip install uvicorn>=0.11.7
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show uvicorn

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2020-7695, inspect your installed packages using pip:

pip show uvicorn

Analyze the terminal output to locate any version of Uvicorn in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.11.7), your application is affected.

Note: The pip show uvicorn command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection'), where the product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component. In Uvicorn, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

Uvicorn before 0.11.7 is vulnerable to HTTP response splitting. CRLF sequences are not escaped in the value of HTTP headers. Attackers can exploit exploit this to add arbitrary headers to HTTP responses, or even return an arbitrary response body, whenever crafted input is used to construct HTTP headers.

CVE-2020-7695 Affected Uvicorn Versions

1 component(s)
Fixed Versions:
0.11.7
Product / Package Ecosystem Affected Versions Fixed Version
uvicorn
pypi/uvicorn
PyPI
< 0.11.7
0.11.7

References

NVD — CVE-2020-7695 NVD
https://nvd.nist.gov/vuln/detail/CVE-2020-7695
Uvicorn Source Repository REPOSITORY
https://github.com/encode/uvicorn
Uvicorn Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/uvicorn/PYSEC-2020-151.yaml
snyk.io/vuln/snyk-python-uv... WEB
https://snyk.io/vuln/SNYK-PYTHON-UVICORN-570471

Frequently Asked Questions

What is CVE-2020-7695?
CVE-2020-7695 is a security vulnerability in Uvicorn involving HTTP response splitting in uvicorn under CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection').
Which Uvicorn versions are affected?
Affected versions include releases prior to 0.11.7 across affected packages: uvicorn.
What version fixes CVE-2020-7695?
Upgrading to 0.11.7 (or the latest patched release for your respective branch) resolves the vulnerability.
Is uvicorn affected?
Yes, uvicorn is affected in releases prior to 0.11.7. Upgrade your dependency to 0.11.7 or later.
What is the CVSS score of CVE-2020-7695?
CVE-2020-7695 has a CVSS v3.1 base score of 7.5 (HIGH) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.
What CWE is associated with CVE-2020-7695?
CVE-2020-7695 is classified under CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') (The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.).
How can I check PyPI dependencies for CVE-2020-7695?
Run the dependency tree command: 'pip show uvicorn'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f97h-2pfx-f59f",
  "modified" : "2024-11-18T22:31:58Z",
  "published" : "2020-07-29T18:07:20Z",
  "aliases" : [ "CVE-2020-7695" ],
  "summary" : "HTTP response splitting in uvicorn",
  "details" : "Uvicorn before 0.11.7 is vulnerable to HTTP response splitting. CRLF sequences are not escaped in the value of HTTP headers. Attackers can exploit exploit this to add arbitrary headers to HTTP responses, or even return an arbitrary response body, whenever crafted input is used to construct HTTP headers.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "uvicorn"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.11.7"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2020-7695"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/encode/uvicorn"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/uvicorn/PYSEC-2020-151.yaml"
  }, {
    "type" : "WEB",
    "url" : "https://snyk.io/vuln/SNYK-PYTHON-UVICORN-570471"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-74" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-07-29T17:37:41Z",
    "nvd_published_at" : "2020-07-27T12:15:00Z"
  }
}