ssh: tighten DH bounds to 1<e<p-1 and add K check#11303
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// Erlang/OTP Github Action Bot |
Tighten e/f validation from inclusive [1, p-1] to strict (1 < e < p-1)
on all plain-DH and GEX paths. Add missing 1 < K < p-1 check on the
plain-DH client path (handle_kexdh_reply), matching what the GEX code
already enforced.
The RFCs (4253 §8, 4419 §3) only require inclusive bounds for e/f, but
OpenSSH and Go both enforce strict bounds. The K check on plain DH is
defense-in-depth — with safe primes and strict e/f, K ∈ {1, p-1} cannot
occur, but the check guards against crypto backend bugs at zero cost.
No interop risk: no legitimate peer sends e ∈ {0, 1, p-1, p}.
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Mikaka27
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Jul 10, 2026
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Tighten e/f validation from inclusive [1, p-1] to strict (1 < e < p-1) on all plain-DH and GEX paths. Add missing 1 < K < p-1 check on the plain-DH client path (handle_kexdh_reply), matching what the GEX code already enforced.
The RFCs (4253 §8, 4419 §3) only require inclusive bounds for e/f, but OpenSSH and Go both enforce strict bounds. The K check on plain DH is defense-in-depth — with safe primes and strict e/f, K ∈ {1, p-1} cannot occur, but the check guards against crypto backend bugs at zero cost.
No interop risk: no legitimate peer sends e ∈ {0, 1, p-1, p}.