CVE-2021-37634

LeafKit allows XSS with untrusted user input

Description

Leafkit is a templating language with Swift-inspired syntax. Versions prior to 1.3.0 are susceptible to Cross-site Scripting (XSS) attacks. This affects anyone passing unsanitised data to Leaf's variable tags. Before this fix, Leaf would not escape any strings passed to tags as variables. If an attacker managed to find a variable that was rendered with their unsanitised data, they could inject scripts into a generated Leaf page, which could enable XSS attacks if other mitigations such as a Content Security Policy were not enabled. This has been patched in 1.3.0. As a workaround sanitize any untrusted input before passing it to Leaf and enable a CSP to block inline script and CSS data.

Category

7.4
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.31%
Third-Party Advisory github.com
Affected: vapor leaf-kit
Published at:
Updated at:

References

Link Tags
https://github.com/vapor/leaf-kit/security/advisories/GHSA-rv3x-xq3r-8j9h third party advisory
https://github.com/vapor/leaf-kit-ghsa-rv3x-xq3r-8j9h/pull/1 broken link

Frequently Asked Questions

What is the severity of CVE-2021-37634?
CVE-2021-37634 has been scored as a high severity vulnerability.
How to fix CVE-2021-37634?
To fix CVE-2021-37634, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-37634 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-37634 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-37634?
CVE-2021-37634 affects vapor leaf-kit.
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