A specially crafted Bitcoin script can cause a discrepancy between the specified SLP consensus rules and the validation result of the slpjs npm package. An attacker could create a specially crafted Bitcoin script in order to cause a hard-fork from the SLP consensus. Affected users can upgrade to any version >= 0.21.4.
https://github.com/simpleledger/slpjs/security/advisories/GHSA-425c-ccf3-3jrr