CVSS3
Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality Impact
NONE
Integrity Impact
HIGH
Availability Impact
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS
Percentile
38.8%
Multiplication of certain unreduced P-256 scalars produce incorrect results.
There are no protocols known at this time that can be attacked due to this.
From the fix commit notes:
Unlike the rest of nistec, the P-256 assembly does not use complete
addition formulas, meaning that p256PointAdd[Affine]Asm won’t return the
correct value if the two inputs are equal.
This was (undocumentedly) ignored in the scalar multiplication loops
because as long as the input point is not the identity and the scalar is
lower than the order of the group, the addition inputs can’t be the same.
As part of the math/big rewrite, we went however from always reducing
the scalar to only checking its length, under the incorrect assumption
that the scalar multiplication loop didn’t require reduction.