diff --git a/arrow-avro/src/reader/block.rs b/arrow-avro/src/reader/block.rs
index e20818bf968a..8df76c4b15f0 100644
--- a/arrow-avro/src/reader/block.rs
+++ b/arrow-avro/src/reader/block.rs
@@ -96,7 +96,13 @@ impl BlockDecoder {
                             AvroError::ParseError(format!("Block size cannot be negative, got {c}"))
                         })?;
 
-                        self.in_progress.data.reserve(self.bytes_remaining);
+                        // Only reserve what the current input backs: the block size is
+                        // input specified so could be an extreme value (e.g. i64::MAX)
+                        // in case of corrupted/malicious input. The rest is reserved
+                        // lazily by `extend_from_slice` below as data arrives.
+                        self.in_progress
+                            .data
+                            .reserve(self.bytes_remaining.min(buf.len()));
                         self.state = BlockDecoderState::Data;
                     }
                 }
@@ -148,3 +154,72 @@ impl BlockDecoder {
         self.bytes_remaining
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Zig-zag encode `value` as an Avro `long` (variable-length integer).
+    fn encode_long(value: i64, out: &mut Vec<u8>) {
+        let mut n = ((value << 1) ^ (value >> 63)) as u64;
+        while n >= 0x80 {
+            out.push((n as u8) | 0x80);
+            n >>= 7;
+        }
+        out.push(n as u8);
+    }
+
+    #[test]
+    fn test_oversized_block_size_bounds_reserve() {
+        // A block advertising `i64::MAX` bytes must not reserve that up front when only
+        // a few payload bytes are present, or a crafted OCF aborts on a huge alloc (#10234).
+        let mut buf = Vec::new();
+        encode_long(1, &mut buf); // object count
+        encode_long(i64::MAX, &mut buf); // attacker-controlled block size
+        buf.extend_from_slice(&[0u8; 8]); // a handful of real bytes
+
+        let mut decoder = BlockDecoder::default();
+        let read = decoder.decode(&buf).unwrap();
+
+        assert_eq!(read, buf.len(), "all available input should be consumed");
+        assert!(
+            decoder.in_progress.data.capacity() <= buf.len(),
+            "capacity {} must stay bounded by available input {}, not the advertised i64::MAX",
+            decoder.in_progress.data.capacity(),
+            buf.len(),
+        );
+    }
+
+    #[test]
+    fn test_negative_block_size_errors() {
+        let mut buf = Vec::new();
+        encode_long(1, &mut buf); // object count
+        encode_long(-1, &mut buf); // invalid (negative) block size
+
+        let mut decoder = BlockDecoder::default();
+        let err = decoder.decode(&buf).unwrap_err();
+        assert!(
+            err.to_string().contains("Block size cannot be negative"),
+            "unexpected error: {err}",
+        );
+    }
+
+    #[test]
+    fn test_well_formed_block_round_trips() {
+        // The capped reserve must not change decoding of a normal block.
+        let payload = [1u8, 2, 3, 4];
+        let sync = [7u8; 16];
+        let mut buf = Vec::new();
+        encode_long(2, &mut buf); // object count
+        encode_long(payload.len() as i64, &mut buf); // block size
+        buf.extend_from_slice(&payload);
+        buf.extend_from_slice(&sync);
+
+        let mut decoder = BlockDecoder::default();
+        assert_eq!(decoder.decode(&buf).unwrap(), buf.len());
+        let block = decoder.flush().expect("a complete block");
+        assert_eq!(block.count, 2);
+        assert_eq!(block.data, payload);
+        assert_eq!(block.sync, sync);
+    }
+}
diff --git a/arrow-avro/src/reader/record.rs b/arrow-avro/src/reader/record.rs
index 306c77718234..2a29ba127e4d 100644
--- a/arrow-avro/src/reader/record.rs
+++ b/arrow-avro/src/reader/record.rs
@@ -2286,35 +2286,58 @@ fn process_blockwise(
         match block_count.cmp(&0) {
             Ordering::Equal => break,
             Ordering::Less => {
-                let count = (-block_count) as usize;
+                // `unsigned_abs` avoids overflowing `-block_count` for `i64::MIN` (#10235)
+                let count = block_count.unsigned_abs() as usize;
                 // A negative count is followed by a long of the size in bytes
-                let size_in_bytes = buf.get_long()? as usize;
+                let raw_size = buf.get_long()?;
+                let size_in_bytes = usize::try_from(raw_size).map_err(|_| {
+                    AvroError::ParseError(format!("Block size cannot be negative, got {raw_size}"))
+                })?;
                 match negative_behavior {
                     NegativeBlockBehavior::ProcessItems => {
                         // Process items one-by-one after reading size
-                        for _ in 0..count {
-                            on_item(buf)?;
-                        }
+                        total = process_block_items(buf, count, total, &mut on_item)?;
                     }
                     NegativeBlockBehavior::SkipBySize => {
                         // Skip the entire block payload at once
                         let _ = buf.get_fixed(size_in_bytes)?;
+                        total = total.saturating_add(count);
                     }
                 }
-                total += count;
             }
             Ordering::Greater => {
                 let count = block_count as usize;
-                for _ in 0..count {
-                    on_item(buf)?;
-                }
-                total += count;
+                total = process_block_items(buf, count, total, &mut on_item)?;
             }
         }
     }
     Ok(total)
 }
 
+/// Decode `count` items, capping the running total at `i32::MAX` (the largest index
+/// an Arrow list/map offset holds). Otherwise a crafted `i64::MAX` count of a zero-byte
+/// item like `null` spins the loop forever (#10235); byte-consuming items self-terminate
+/// on cursor exhaustion, so valid blocks (including `array<null>`) are unaffected.
+#[inline]
+fn process_block_items(
+    buf: &mut AvroCursor,
+    count: usize,
+    total: usize,
+    on_item: &mut impl FnMut(&mut AvroCursor) -> Result<(), AvroError>,
+) -> Result<usize, AvroError> {
+    let new_total = total.checked_add(count).filter(|&t| t <= i32::MAX as usize);
+    let Some(new_total) = new_total else {
+        return Err(AvroError::ParseError(format!(
+            "Array/map item count {count} exceeds the maximum {} addressable by 32-bit offsets",
+            i32::MAX
+        )));
+    };
+    for _ in 0..count {
+        on_item(buf)?;
+    }
+    Ok(new_total)
+}
+
 #[inline]
 fn flush_values<T>(values: &mut Vec<T>) -> Vec<T> {
     std::mem::replace(values, Vec::with_capacity(DEFAULT_CAPACITY))
@@ -3434,6 +3457,62 @@ mod tests {
         assert_eq!(values.value(2), 3);
     }
 
+    /// Zig-zag + unsigned-LEB128 encode, correct for all `i64` including `MIN`/`MAX`
+    /// (`encode_avro_long` loops forever on those two values).
+    fn encode_avro_long_extreme(value: i64) -> Vec<u8> {
+        let mut n = ((value << 1) ^ (value >> 63)) as u64;
+        let mut out = Vec::new();
+        while n >= 0x80 {
+            out.push((n as u8) | 0x80);
+            n >>= 7;
+        }
+        out.push(n as u8);
+        out
+    }
+
+    // `array<null>` is the worst case: items consume no bytes, so an unbounded
+    // `block_count` spins the item loop without ever advancing the cursor (#10235).
+    fn array_of_null_decoder() -> Decoder {
+        let list_dt = avro_from_codec(Codec::List(Arc::new(avro_from_codec(Codec::Null))));
+        Decoder::try_new(&list_dt).unwrap()
+    }
+
+    #[test]
+    fn test_array_of_null_decodes() {
+        // A valid `array<null>` still decodes: zero-byte items make the count exceed the
+        // bytes left, so the bound must not reject it (#10235 review).
+        let mut decoder = array_of_null_decoder();
+        let mut data = encode_avro_long(3); // three null items
+        data.extend_from_slice(&encode_avro_long(0)); // empty-block terminator
+        decoder.decode(&mut AvroCursor::new(&data)).unwrap();
+    }
+
+    #[test]
+    fn test_array_block_count_i64_max_errors() {
+        // A positive `i64::MAX` block count must error rather than spin the item loop.
+        let mut decoder = array_of_null_decoder();
+        let mut data = encode_avro_long_extreme(i64::MAX); // item count
+        data.extend_from_slice(&encode_avro_long(0)); // empty-block terminator
+        let err = decoder.decode(&mut AvroCursor::new(&data)).unwrap_err();
+        assert!(
+            err.to_string().contains("exceeds the maximum"),
+            "unexpected error: {err}",
+        );
+    }
+
+    #[test]
+    fn test_array_block_count_i64_min_errors() {
+        // `i64::MIN` previously overflowed `-block_count` before spinning the loop.
+        let mut decoder = array_of_null_decoder();
+        let mut data = encode_avro_long_extreme(i64::MIN); // negative item count
+        data.extend_from_slice(&encode_avro_long(0)); // block size in bytes
+        let err = decoder.decode(&mut AvroCursor::new(&data)).unwrap_err();
+        assert!(
+            err.to_string().contains("exceeds the maximum"),
+            "unexpected error: {err}",
+        );
+    }
+
     #[test]
     fn test_nested_array_decoding() {
         let inner_ty = avro_from_codec(Codec::List(Arc::new(avro_from_codec(Codec::Int32))));