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CVE-2018-7753

Bleach URI Scheme Restriction Bypass

9.8 CriticalFix available

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
High
Integrity
High
Availability
High

Exploit likelihood

2.17%Up 1.3 points since Apr 14, 2021
90%50%10%1%

What each source reports

NVD Score used 9.8

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.

Record
CVE-2018-7753
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
CVSS 2.0
7.5 HighAV:N/AC:L/Au:N/C:P/I:P/A:P
Weakness
CWE-20
Updated
2026-11-02
CVE List No score

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.

Record
CVE-2018-7753
Updated
2026-11-02
EUVDEUVD-2018-0026 No score

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.

Record
EUVD-2018-0026
Updated
2026-11-03
GitHub AdvisoriesGHSA-m9mq-p2f9-cfqv 9.3

Bleach URI Scheme Restriction Bypass

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.

Record
GHSA-m9mq-p2f9-cfqv
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-20
Updated
2026-11-02
OSV 9.8

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.

Record
CVE-2018-7753
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVDEBIAN-CVE-2018-7753 9.8

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.

Record
DEBIAN-CVE-2018-7753
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
Show 7 moreShow less
OSVGHSA-m9mq-p2f9-cfqv 9.3

Bleach URI Scheme Restriction Bypass

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.

Record
GHSA-m9mq-p2f9-cfqv
CVSS 4.0
9.3 CriticalCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Weakness
CWE-20
Updated
2026-11-02
OSVUBUNTU-CVE-2018-7753 9.8

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.

Record
UBUNTU-CVE-2018-7753
CVSS 3.0
9.8 CriticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Updated
2026-11-02
OSVopenSUSE-SU-2024:11219-1 No score

python36-bleach-3.3.0-1.4 on GA media

These are all security issues fixed in the python36-bleach-3.3.0-1.4 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:11219-1
Updated
2026-11-02
OSVopenSUSE-SU-2024:14134-1 No score

python310-bleach-6.1.0-1.5 on GA media

These are all security issues fixed in the python310-bleach-6.1.0-1.5 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2024:14134-1
Updated
2026-11-02
OSVopenSUSE-SU-2026:11323-1 No score

python313-bleach-6.4.0-1.1 on GA media

These are all security issues fixed in the python313-bleach-6.4.0-1.1 package on the GA media of openSUSE Tumbleweed.

Record
openSUSE-SU-2026:11323-1
Updated
2026-11-02
OSVPYSEC-2018-51 No score

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.

Record
PYSEC-2018-51
Updated
2026-11-02
OSVUSN-8077-1 No score

python-bleach vulnerabilities

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 Michał 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)

Record
USN-8077-1
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
bleach
PyPI
2.1.0 up to 2.1.3
2.1.3
python-bleach
Debian:12
before 2.1.3-1
2.1.3-1
python-bleach
Debian:13
before 2.1.3-1
2.1.3-1
python-bleach
Debian:14
before 2.1.3-1
2.1.3-1
bleach
PyPI
2.1.0 up to 2.1.3, plus listed versions
2.12.1.12.1.2
2.1.3
bleach
PyPI
2.1 up to 2.1.3, plus listed versions
2.1.12.1.2
2.1.3
python-bleach
Ubuntu:Pro:18.04:LTS
before 2.1.2-1ubuntu0.1~esm1, plus listed versions
2.0-12.1.2-1
2.1.2-1ubuntu0.1~esm1
python-bleach
Ubuntu:Pro:16.04:LTS
before 1.4.2-1ubuntu0.1~esm1, plus listed versions
1.4-11.4.2-1
1.4.2-1ubuntu0.1~esm1
python-bleach
Ubuntu:Pro:20.04:LTS
before 3.1.1-1ubuntu0.1~esm1, plus listed versions
3.1.0-13.1.0-23.1.1-1
3.1.1-1ubuntu0.1~esm1
python-bleach
openSUSE:Tumbleweed
From an advisory covering 5 CVEs
before 6.1.0-1.5
6.1.0-1.5
python-bleach
openSUSE:Tumbleweed
From an advisory covering 5 CVEs
before 6.4.0-1.1
6.4.0-1.1

History

History
RecordedChangedSources
affected, facts
aliasesEUVD
first indexedCVE List, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2018-7753 is a critical vulnerability (CVSS 9.8) in Mozilla Bleach, published March 7, 2018. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 2.17%, the 82nd percentile. Fixed in bleach 2.1.3.

References

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