XSS in Vapor Leaf-Kit
CVE-2021-37634
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.
Vulnerability class: XSS (Cross-Site Scripting)
EPSS: 0.007 (49.8th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 7.4 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:N/A:N.
Affected products
- Vapor Leaf-kit — versions < 1.3.0
- Vapor Leafkit
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Third Party Advisory)
- security-advisories@github.com (x_refsource_MISC, Broken Link)
Frequently asked questions
- What is CVE-2021-37634?
- CVE-2021-37634 is a high-severity vulnerability in Vapor Leaf-Kit, classified under Cross-site Scripting. CVSS score: 7.4/10. Published 2021-08-09.
- How severe is CVE-2021-37634?
- High severity. CVSS v3 base score is 7.4 out of 10.