The vulnerability in Bouncy Castle for Java prior to version 1.85 and LTS prior to 2.73.12 involves an error in the RSA PKCS#1 signature verification routine. Specifically, when the NULL byte is omitted in the signature encoding, the verification process skips the last two bytes of the hash, potentially allowing malformed signatures to be accepted as valid. This is classified under CWE-347, indicating improper verification of cryptographic signatures.

This vulnerability undermines the integrity guarantees provided by RSA PKCS#1 signature verification in affected versions of Bouncy Castle for Java. An attacker could exploit this flaw to bypass signature validation, potentially allowing unauthorized code or data to be accepted as authentic. No known exploits are reported in the wild at this time.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Users should monitor official Bouncy Castle advisories for updates and apply any released patches promptly. Until a fix is available, avoid using affected versions in security-critical contexts or implement additional signature verification controls if feasible.