fix: do not negotiate TLS 1.3 when only TLS 1.2 ciphers are supplied#303
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zookzook merged 1 commit intoMay 27, 2026
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When the caller passes `ssl_opts.ciphers` without an explicit `ssl_opts.versions`, Erlang's `:ssl` will still attempt TLS 1.3 negotiation if the OTP build supports it. If none of the supplied ciphers match a TLS 1.3 suite, the handshake fails with no automatic fallback to TLS 1.2. In practice this surfaces when the MongoDB server starts negotiating TLS 1.3 (e.g. after a cluster upgrade) and the user's `:ciphers` list only contains TLS-1.2-era suites. `Mongo.MongoDBConnection.Utils.maybe_restrict_versions/1` detects the mismatch and pins `:versions` to `[:"tlsv1.2"]` when the supplied ciphers do not include any TLS 1.3 suite. Callers who explicitly set `:versions` are left untouched. The override is logged at `Logger.warning` so operators see it in production where info-level logs are typically filtered. Also normalizes `opts[:ssl_opts]` to `[]` on the IP-address branch of `defp ssl/2`; previously that branch could pass `nil` to `:ssl.connect/3` if the caller omitted `:ssl_opts`. Unit tests cover charlist / atom / binary / map cipher shapes, mixed TLS 1.2 + TLS 1.3 lists, and the no-op cases (`:ciphers` nil/empty, `:versions` already set). Tests skip cleanly on OTP builds without TLS 1.3.
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Thanks for this nice PR. |
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When the caller passes
ssl_opts.cipherswithout an explicitssl_opts.versions, Erlang's:sslwill still attempt TLS 1.3 negotiation if the OTP build supports it. If none of the supplied ciphers match a TLS 1.3 suite, the handshake fails with no automatic fallback to TLS 1.2.In practice this surfaces when the MongoDB server starts negotiating TLS 1.3 (e.g. after a cluster upgrade) and the user's
:cipherslist only contains TLS-1.2-era suites.Mongo.MongoDBConnection.Utils.maybe_restrict_versions/1detects the mismatch and pins:versionsto[:"tlsv1.2"]when the supplied ciphers do not include any TLS 1.3 suite. Callers who explicitly set:versionsare left untouched. The override is logged atLogger.warningso operators see it in production where info-level logs are typically filtered.Also normalizes
opts[:ssl_opts]to[]on the IP-address branch ofdefp ssl/2; previously that branch could passnilto:ssl.connect/3if the caller omitted:ssl_opts.Unit tests cover charlist / atom / binary / map cipher shapes, mixed TLS 1.2 + TLS 1.3 lists, and the no-op cases (
:ciphersnil/empty,:versionsalready set).