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Critical

Bleach URI Scheme Restriction Bypass

  • Disclosed: 07.03.2018
  • Updated: 11.10.2026 12:19

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.

Affected software

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PlatformPackageVulnerable versionsFixed in
Python (PyPI) bleach >= 2.1.0, < 2.1.3 2.1.3

References

CVSS score 9.8/10
CVSS vector
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE)
CWE-20
Platform
Python (PyPI)
Package
bleach
Disclosed
07.03.2018
Updated
11.10.2026 12:19

Sources and licenses

OSV / GitHub Advisory Database - PYSEC-2018-51 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-m9mq-p2f9-cfqv - CC BY 4.0

Vulnerability history: bleach

All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.

Total entries
8
First → latest
03.2018 06.2026
Without a fix
1
Exploited in attacks
0

Severity breakdown

  • Critical 1
  • High 1
  • Medium 5
  • Low 1

Disclosures per year

  1. Bleach clean() / Cleaner() fails to sanitize dangerous URI schemes in allowed formaction attributes
    Medium · 6.1 ghsa-gj48-438w-jh9v < 6.4.0 6.4.0
  2. Bleach linkify(parse_email=True) CPU exhaustion via unbounded email regex scanning
    Medium · 4.3 ghsa-g75f-g53v-794x = 6.3.0 no fix
  3. Bleach: URI sanitization allows disallowed URI schemes with Unicode > U+00A0 in output
    Low · 0.0 ghsa-8rfp-98v4-mmr6 < 6.4.0 6.4.0
  4. Cross-site scripting in Bleach
    Medium · 6.1 CVE-2021-23980 < 3.3.0 3.3.0
  5. regular expression denial-of-service (ReDoS) in Bleach
    High · 7.5 CVE-2020-6817 < 3.1.4 3.1.4
  6. Bleach vulnerable to mutation XSS via whitelisted math or svg and raw tag
    Medium · 6.1 CVE-2020-6816 < 3.1.2 3.1.2
  7. XSS in Bleach when noscript and raw tag whitelisted
    Medium · 6.1 CVE-2020-6802 < 3.1.1 3.1.1
  8. Bleach URI Scheme Restriction Bypass this entry
    Critical · 9.8 CVE-2018-7753 >= 2.1.0, < 2.1.3 2.1.3

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