CVE-2018-7753: Bleach Bleach URI Scheme Restriction Bypass Vulnerability

CRITICAL
Advisory Identifier: GHSA-m9mq-p2f9-cfqv
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CVSS 9.8
CWE-20
Published
Advisory Summary

CVE-2018-7753 is a CRITICAL (CVSS 9.8) bleach uri scheme restriction bypass vulnerability (CWE-20: Improper Input Validation) affecting Bleach libraries in the PyPI ecosystem. The issue involves bleach uri scheme restriction bypass. Remediation is available by upgrading affected packages to version 2.1.3.

CVE-2018-7753 at a Glance

CVE Identifier CVE-2018-7753
GHSA Identifier GHSA-m9mq-p2f9-cfqv
Severity CRITICAL
CVSS v3.1 Base Score 9.8
CWE Classification CWE-20: Improper Input Validation
Affected Product Bleach
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 9.8

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H).

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 High (C:H)
Integrity High (I:H)
Availability High (A:H)

How to Fix CVE-2018-7753

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

bleach fixed: 2.1.3 
pip install bleach>=2.1.3
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 bleach

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2018-7753, inspect your installed packages using pip:

pip show bleach

Analyze the terminal output to locate any version of Bleach in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 2.1.3), your application is affected.

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

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-20: Improper Input Validation, where the product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. In Bleach, 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

An issue was discovered in Bleach 2.1.x before 2.1.3. Attributes that have URI values weren't properly sanitized if the values contained character entities. Using character entities, it was possible to construct a URI value with a scheme that was not allowed that would slide through unsanitized.

CVE-2018-7753 Affected Bleach Versions

1 component(s)
Fixed Versions:
2.1.3
Product / Package Ecosystem Affected Versions Fixed Version
bleach
pypi/bleach
PyPI
≥ 2.1.0
< 2.1.3
2.1.3

References

NVD — CVE-2018-7753 NVD
https://nvd.nist.gov/vuln/detail/CVE-2018-7753
Security Fix Commit FIX COMMIT
https://github.com/mozilla/bleach/commit/c5df5789ec3471a31311f42c2d19fc2cf21b35ef
bugs.debian.org/892252 WEB
https://bugs.debian.org/892252
Bleach Source Repository REPOSITORY
https://github.com/mozilla/bleach
Bleach Release RELEASE
https://github.com/mozilla/bleach/releases/tag/v2.1.3
Bleach Source Repository REPOSITORY
https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2018-51.yaml

Frequently Asked Questions

What is CVE-2018-7753?
CVE-2018-7753 is a security vulnerability in Bleach involving Bleach URI Scheme Restriction Bypass under CWE-20: Improper Input Validation.
Which Bleach versions are affected?
Affected versions include releases prior to 2.1.3 across affected packages: bleach.
What version fixes CVE-2018-7753?
Upgrading to 2.1.3 (or the latest patched release for your respective branch) resolves the vulnerability.
Is bleach affected?
Yes, bleach is affected in releases prior to 2.1.3. Upgrade your dependency to 2.1.3 or later.
What is the CVSS score of CVE-2018-7753?
CVE-2018-7753 has a CVSS v3.1 base score of 9.8 (CRITICAL) with vector string CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.
What CWE is associated with CVE-2018-7753?
CVE-2018-7753 is classified under CWE-20: Improper Input Validation (The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.).
How can I check PyPI dependencies for CVE-2018-7753?
Run the dependency tree command: 'pip show bleach'. 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-m9mq-p2f9-cfqv",
  "modified" : "2024-09-04T19:41:50Z",
  "published" : "2019-01-04T17:46:30Z",
  "aliases" : [ "CVE-2018-7753" ],
  "summary" : "Bleach URI Scheme Restriction Bypass",
  "details" : "An issue was discovered in Bleach 2.1.x before 2.1.3. Attributes that have URI values weren't properly sanitized if the values contained character entities. Using character entities, it was possible to construct a URI value with a scheme that was not allowed that would slide through unsanitized.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H"
  }, {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "bleach"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "2.1.0"
      }, {
        "fixed" : "2.1.3"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2018-7753"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mozilla/bleach/commit/c5df5789ec3471a31311f42c2d19fc2cf21b35ef"
  }, {
    "type" : "WEB",
    "url" : "https://bugs.debian.org/892252"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/mozilla/bleach"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/mozilla/bleach/releases/tag/v2.1.3"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/pypa/advisory-database/tree/main/vulns/bleach/PYSEC-2018-51.yaml"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-20" ],
    "severity" : "CRITICAL",
    "github_reviewed" : true,
    "github_reviewed_at" : "2020-06-16T21:45:43Z",
    "nvd_published_at" : null
  }
}