Fix CVE-2023-50980 in BERDecodeGF2NP - #1356
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The BER decoder for F(2^m) curve parameters accepted invalid reduction polynomial exponents and did not bound m before constructing the PolynomialMod2 representation. Malformed input could therefore reach PolynomialMod2::Trinomial or Pentanomial, where the runtime checks are relaxed for ECIES<EC2N> compatibility. An unbounded m value could also drive a large bit-vector allocation. Move validation to the decode boundary. Require 0 < t1 < m for trinomials, 0 < t3 < t2 < t1 < m for pentanomials, and cap m at 4096. The cap covers B-571 with plenty of headroom.
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Summary
Fixes CVE-2023-50980.
BERDecodeGF2NPaccepted invalid reduction-polynomial exponents for F(2^m) curve parameters and did not bound the field degreembefore constructing thePolynomialMod2representation.Malformed input could reach
PolynomialMod2::TrinomialorPolynomialMod2::Pentanomial, where the runtime checks are relaxed forECIES<EC2N>compatibility. An unboundedmvalue could also drive a large bit-vector allocation.This validates the values before constructing the
PolynomialMod2representation:
0 < t1 < mfor trinomials0 < t3 < t2 < t1 < mfor pentanomialsmatMAX_GF2N_FIELD_DEGREE = 4096The cap covers B-571 with headroom.
What changed
minBERDecodeGF2NP