GO-2026-5048

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GO-2026-5048

Summary: Denial of service via unbounded map allocations in github.com/iskorotkov/avro/v2 and github.com/hamba/avro/v2

Details: The Avro map decoder accepts attacker-controlled block-element counts from the wire format and grows the destination map without enforcing an upper bound. A producer can declare an arbitrarily large map (in one block, or chunked across many sub-limit blocks) and exhaust process memory until the OOM killer fires. The fix introduces Config.MaxMapAllocSize with cumulative enforcement across block boundaries. The new limit is opt-in: the field defaults to zero, which preserves the previous unbounded behavior for backward compatibility. Upgrading to v2.33.0 alone does not mitigate the issue; consumers of untrusted Avro data must explicitly set MaxMapAllocSize on their avro.Config.

References: https://github.com/iskorotkov/avro/security/advisories/GHSA-mx64-mj3q-7prj, https://github.com/iskorotkov/avro/commit/5192df96a158999344ac96ebcb1f7461d626f6d7