CVE-2021-20305: High severity IBM Security Verify Access vulnerability
A flaw was found in Nettle in versions before 3.7.2, where several Nettle signature verification functions (GOST DSA, EDDSA & ECDSA) result in the Elliptic Curve Cryptography point (ECC) multiply function being called with out-of-range scalers, possibly resulting in incorrect results. This flaw allows an attacker to force an invalid signature, causing an assertion failure or possible validation. The highest threat to this vulnerability is to confidentiality, integrity, as well as system availability.
Other sources
Certain signatures result in the ecc point multiply function being called with out-of-range scalars, which may give incorrect results, or crash in an assertion failure. It's an old bug, probably since Nettle's initial implementation of ECDSA.
Even when it's not possible to trigger an assertion failure, it's easy to produce valid-looking input "signatures" that hit out-of range intermediate scalar values where point multiplication may misbehave. This applies to all the NIST secp curves as well as the GOST curves.
Reference: https://lists.lysator.liu.se/pipermail/nettle-bugs/2021/009457.html
— Red Hat
Nettle could allow a remote attacker to bypass security restrictions, caused by a flaw related to several signature verification functions result in the Elliptic Curve Cryptography point (ECC) multiply function being invoked with out-of-range scalers. An attacker could exploit this vulnerability to force an invalid signature, causing an assertion failure or possible validation.
— IBM