CVSS2
Attack Vector
NETWORK
Attack Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:M/Au:N/C:P/I:P/A:P
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
EPSS
Percentile
50.0%
When HTML is sanitized using Sanitize’s “relaxed” config or a custom config that allows certain elements, some content in a <math>
or <svg>
element may not be sanitized correctly even if math
and svg
are not in the allowlist.
You are likely to be vulnerable to this issue if you use Sanitize’s relaxed config or a custom config that allows one or more of the following HTML elements:
iframe
math
noembed
noframes
noscript
plaintext
script
style
svg
xmp
Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize, potentially resulting in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.
This problem has been fixed in Sanitize 5.2.1.
If upgrading is not possible, a workaround is to override the default value of Sanitize’s :remove_contents
config option with the following value, which ensures that the contents of math
and svg
elements (among others) are removed entirely when those elements are not in the allowlist:
%w[iframe math noembed noframes noscript plaintext script style svg xmp]
For example, if you currently use Sanitize’s relaxed config, you can create a custom config object that overrides the default value of :remove_contents
like this:
custom_config = Sanitize::Config.merge(
Sanitize::Config::RELAXED,
:remove_contents => %w[iframe math noembed noframes noscript plaintext script style svg xmp]
)
You would then pass this custom config to Sanitize when sanitizing HTML.
If you have any questions or comments about this advisory:
Many thanks to Michal Bentkowski of Securitum for reporting this bug and helping to verify the fix.
Vendor | Product | Version | CPE |
---|---|---|---|
sanitize_project | sanitize | * | cpe:2.3:a:sanitize_project:sanitize:*:*:*:*:*:ruby:*:* |
github.com/advisories/GHSA-p4x4-rw2p-8j8m
github.com/rgrove/sanitize/commit/a11498de9e283cd457b35ee252983662f7452aa9
github.com/rgrove/sanitize/releases/tag/v5.2.1
github.com/rgrove/sanitize/security/advisories/GHSA-p4x4-rw2p-8j8m
github.com/rubysec/ruby-advisory-db/blob/master/gems/sanitize/CVE-2020-4054.yml
nvd.nist.gov/vuln/detail/CVE-2020-4054
usn.ubuntu.com/4543-1/
www.debian.org/security/2020/dsa-4730
CVSS2
Attack Vector
NETWORK
Attack Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
AV:N/AC:M/Au:N/C:P/I:P/A:P
CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
LOW
Integrity Impact
LOW
Availability Impact
LOW
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
EPSS
Percentile
50.0%