Niels Möller reports:
I've prepared a new bug-fix release of Nettle, a low-level
cryptographics library, to fix a serious bug in the function to
verify ECDSA signatures. Implications include an assertion failure,
which could be used for denial-of-service, when verifying signatures
on the secp_224r1 and secp521_r1 curves.
Even when no assert is triggered in ecdsa_verify, ECC point
multiplication may get invalid intermediate values as input, and
produce incorrect results. [...] It appears difficult to construct
an alleged signature that makes the function misbehave in such a way
that an invalid signature is accepted as valid, but such attacks
can't be ruled out without further analysis.