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GHSA-m6xf-fq7q-8743

MediumCVSS 6.1 / 10
Published Mar 24, 2020·Last modified Mar 13, 2026
Affected Components(0)

No affected components available

Description

Impact

A mutation XSS affects users calling bleach.clean with all of:

  • the svg or math in the allowed/whitelisted tags
  • an RCDATA tag (see below) in the allowed/whitelisted tags
  • the keyword argument strip=False

Patches

Users are encouraged to upgrade to bleach v3.1.2 or greater.

Workarounds

  • modify bleach.clean calls to use strip=True, or not whitelist math or svg tags and one or more of the following tags:
script
noscript
style
noframes
xmp
noembed
iframe

References

  • https://bugzilla.mozilla.org/show_bug.cgi?id=1621692
  • https://cure53.de/fp170.pdf
  • https://nvd.nist.gov/vuln/detail/CVE-2020-6816
  • https://www.checkmarx.com/blog/vulnerabilities-discovered-in-mozilla-bleach

Credits

  • Reported by Yaniv Nizry from the CxSCA AppSec group at Checkmarx

For more information

If you have any questions or comments about this advisory:

Risk Scores
Base Score
6.1

The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.

Threat Intelligence
5.6

Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.

EPSS
1.30%

The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.

Exploit
Not available

We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.

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