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.

The remote Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS host has packages installed that are affected by multiple vulnerabilities as referenced in the USN-8077-1 advisory.

    It was discovered that Bleach did not properly sanitize URI attributes containing character entities. An     attacker could possibly use this issue to construct a URI with a disallowed scheme that would bypass     sanitization, leading to cross-site scripting. This issue only affected Ubuntu 18.04 LTS. (CVE-2018-7753)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing     HTML with the noscript tag and a raw tag in the allowed tags list. An attacker could possibly use this     issue to inject malicious content, leading to cross-site scripting. This issue only affected Ubuntu 18.04     LTS. (CVE-2020-6802)

    Yaniv Nizry discovered that Bleach was vulnerable to a mutation cross-site scripting issue when sanitizing     HTML with RCDATA together with svg or math tags in the allowed tags list. An attacker could possibly use     this issue to inject malicious content, leading to cross-site scripting. (CVE-2020-6816)

    It was discovered that Bleach incorrectly handled parsing of style attributes when sanitizing HTML. An     attacker could possibly use this issue to perform a regular expression denial of service, leading to     excessive resource consumption. (CVE-2020-6817)

    Yaniv Nizry and Micha Bentkowski discovered that Bleach was vulnerable to a mutation cross-site     scripting issue when sanitizing HTML with certain combinations of allowed tags. An attacker could possibly     use this issue to inject malicious content, leading to cross-site scripting. (CVE-2021-23980)

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

Version 2.1.3 (March 5th, 2018)

-------------------------------

**Security fixes**

  - 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.

    This security issue was introduced in Bleach 2.1. Anyone     using Bleach 2.1 is highly encouraged to upgrade.

**Backwards incompatible changes**

None

**Features**

None

**Bug fixes**

  - Fixed some other edge cases for attribute URI value     sanitizing and improved testing of this code.

Note that Tenable Network Security has extracted the preceding description block directly from the Fedora update system website.
Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
301534	Ubuntu 16.04 LTS / 18.04 LTS / 20.04 LTS : Bleach vulnerabilities (USN-8077-1)	Nessus	Ubuntu Local Security Checks	critical
120643	Fedora 28 : python-bleach (2018-994424b810)	Nessus	Fedora Local Security Checks	critical

Detections

Analytics

CVE-2018-7753

critical

Tenable Plugins

critical

critical