diff --git a/src/Common/BinStringDecodeHelper.h b/src/Common/BinStringDecodeHelper.h
index df3e014cfad..03c175fd37f 100644
--- a/src/Common/BinStringDecodeHelper.h
+++ b/src/Common/BinStringDecodeHelper.h
@@ -5,7 +5,7 @@
 namespace DB
 {
 
-static void inline hexStringDecode(const char * pos, const char * end, char *& out, size_t word_size = 2)
+static void inline hexStringDecode(const char * pos, const char * end, char *& out, size_t word_size)
 {
     if ((end - pos) & 1)
     {
@@ -23,7 +23,7 @@ static void inline hexStringDecode(const char * pos, const char * end, char *& o
     ++out;
 }
 
-static void inline binStringDecode(const char * pos, const char * end, char *& out)
+static void inline binStringDecode(const char * pos, const char * end, char *& out, size_t word_size)
 {
     if (pos == end)
     {
@@ -53,7 +53,7 @@ static void inline binStringDecode(const char * pos, const char * end, char *& o
         ++out;
     }
 
-    assert((end - pos) % 8 == 0);
+    chassert((end - pos) % word_size == 0);
 
     while (end - pos != 0)
     {
diff --git a/src/Functions/FunctionsBinaryRepresentation.cpp b/src/Functions/FunctionsBinaryRepresentation.cpp
index 0f3f8be96a7..ab10d402df4 100644
--- a/src/Functions/FunctionsBinaryRepresentation.cpp
+++ b/src/Functions/FunctionsBinaryRepresentation.cpp
@@ -3,14 +3,14 @@
 #include <Columns/ColumnString.h>
 #include <Columns/ColumnVector.h>
 #include <Columns/ColumnsNumber.h>
-#include <Common/BitHelpers.h>
-#include <Common/BinStringDecodeHelper.h>
 #include <DataTypes/DataTypeString.h>
 #include <Functions/FunctionFactory.h>
 #include <Functions/IFunction.h>
 #include <IO/WriteHelpers.h>
 #include <Interpreters/Context_fwd.h>
 #include <Interpreters/castColumn.h>
+#include <Common/BinStringDecodeHelper.h>
+#include <Common/BitHelpers.h>
 
 namespace DB
 {
@@ -218,10 +218,7 @@ struct UnbinImpl
     static constexpr auto name = "unbin";
     static constexpr size_t word_size = 8;
 
-    static void decode(const char * pos, const char * end, char *& out)
-    {
-        binStringDecode(pos, end, out);
-    }
+    static void decode(const char * pos, const char * end, char *& out) { binStringDecode(pos, end, out, word_size); }
 };
 
 /// Encode number or string to string with binary or hexadecimal representation
@@ -651,7 +648,15 @@ public:
 
             size_t size = in_offsets.size();
             out_offsets.resize(size);
-            out_vec.resize(in_vec.size() / word_size + size);
+
+            size_t max_out_len = 0;
+            for (size_t i = 0; i < in_offsets.size(); ++i)
+            {
+                const size_t len = in_offsets[i] - (i == 0 ? 0 : in_offsets[i - 1])
+                    - /* trailing zero symbol that is always added in ColumnString and that is ignored while decoding */ 1;
+                max_out_len += (len + word_size - 1) / word_size + /* trailing zero symbol that is always added by Impl::decode */ 1;
+            }
+            out_vec.resize(max_out_len);
 
             char * begin = reinterpret_cast<char *>(out_vec.data());
             char * pos = begin;
@@ -661,6 +666,7 @@ public:
             {
                 size_t new_offset = in_offsets[i];
 
+                /// `new_offset - 1` because in ColumnString each string is stored with trailing zero byte
                 Impl::decode(reinterpret_cast<const char *>(&in_vec[prev_offset]), reinterpret_cast<const char *>(&in_vec[new_offset - 1]), pos);
 
                 out_offsets[i] = pos - begin;
@@ -668,6 +674,9 @@ public:
                 prev_offset = new_offset;
             }
 
+            chassert(
+                static_cast<size_t>(pos - begin) <= out_vec.size(),
+                fmt::format("too small amount of memory was preallocated: needed {}, but have only {}", pos - begin, out_vec.size()));
             out_vec.resize(pos - begin);
 
             return col_res;
@@ -680,11 +689,11 @@ public:
             ColumnString::Offsets & out_offsets = col_res->getOffsets();
 
             const ColumnString::Chars & in_vec = col_fix_string->getChars();
-            size_t n = col_fix_string->getN();
+            const size_t n = col_fix_string->getN();
 
             size_t size = col_fix_string->size();
             out_offsets.resize(size);
-            out_vec.resize(in_vec.size() / word_size + size);
+            out_vec.resize(((n + word_size - 1) / word_size + /* trailing zero symbol that is always added by Impl::decode */ 1) * size);
 
             char * begin = reinterpret_cast<char *>(out_vec.data());
             char * pos = begin;
@@ -694,6 +703,7 @@ public:
             {
                 size_t new_offset = prev_offset + n;
 
+                /// here we don't subtract 1 from `new_offset` because in ColumnFixedString strings are stored without trailing zero byte
                 Impl::decode(reinterpret_cast<const char *>(&in_vec[prev_offset]), reinterpret_cast<const char *>(&in_vec[new_offset]), pos);
 
                 out_offsets[i] = pos - begin;
@@ -701,6 +711,9 @@ public:
                 prev_offset = new_offset;
             }
 
+            chassert(
+                static_cast<size_t>(pos - begin) <= out_vec.size(),
+                fmt::format("too small amount of memory was preallocated: needed {}, but have only {}", pos - begin, out_vec.size()));
             out_vec.resize(pos - begin);
 
             return col_res;
diff --git a/src/Parsers/ExpressionElementParsers.cpp b/src/Parsers/ExpressionElementParsers.cpp
index 5997452bcf3..d4fc9a4bc4d 100644
--- a/src/Parsers/ExpressionElementParsers.cpp
+++ b/src/Parsers/ExpressionElementParsers.cpp
@@ -1129,11 +1129,11 @@ inline static bool makeHexOrBinStringLiteral(IParser::Pos & pos, ASTPtr & node,
 
     if (hex)
     {
-        hexStringDecode(str_begin, str_end, res_pos);
+        hexStringDecode(str_begin, str_end, res_pos, word_size);
     }
     else
     {
-        binStringDecode(str_begin, str_end, res_pos);
+        binStringDecode(str_begin, str_end, res_pos, word_size);
     }
 
     return makeStringLiteral(pos, node, String(reinterpret_cast<char *>(res.data()), (res_pos - res_begin - 1)));
diff --git a/tests/queries/0_stateless/03199_unbin_buffer_overflow.reference b/tests/queries/0_stateless/03199_unbin_buffer_overflow.reference
new file mode 100644
index 00000000000..e69de29bb2d
diff --git a/tests/queries/0_stateless/03199_unbin_buffer_overflow.sh b/tests/queries/0_stateless/03199_unbin_buffer_overflow.sh
new file mode 100755
index 00000000000..337debebb14
--- /dev/null
+++ b/tests/queries/0_stateless/03199_unbin_buffer_overflow.sh
@@ -0,0 +1,33 @@
+#!/usr/bin/env bash
+
+CURDIR=$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)
+# shellcheck source=../shell_config.sh
+. "$CURDIR"/../shell_config.sh
+
+
+# check for buffer overflow in unbin (due to not enough memory preallocate for output buffer)
+# we iterate over all remainders of input string length modulo word_size and check that no assertions are triggered
+
+word_size=8
+for i in $(seq 1 $((word_size+1))); do
+  str=$(printf "%${i}s" | tr ' ' 'x')
+  $CLICKHOUSE_CLIENT -q "SELECT count() FROM numbers(99) GROUP BY unbin(toFixedString(materialize('$str'), $i)) WITH ROLLUP WITH TOTALS FORMAT NULL"
+done
+
+word_size=8
+for i in $(seq 1 $((word_size+1))); do
+  str=$(printf "%${i}s" | tr ' ' 'x')
+  $CLICKHOUSE_CLIENT -q "SELECT count() FROM numbers(99) GROUP BY unbin(materialize('$str')) WITH ROLLUP WITH TOTALS FORMAT NULL"
+done
+
+word_size=2
+for i in $(seq 1 $((word_size+1))); do
+  str=$(printf "%${i}s" | tr ' ' 'x')
+  $CLICKHOUSE_CLIENT -q "SELECT count() FROM numbers(99) GROUP BY unhex(toFixedString(materialize('$str'), $i)) WITH ROLLUP WITH TOTALS FORMAT NULL"
+done
+
+word_size=2
+for i in $(seq 1 $((word_size+1))); do
+  str=$(printf "%${i}s" | tr ' ' 'x')
+  $CLICKHOUSE_CLIENT -q "SELECT count() FROM numbers(99) GROUP BY unhex(materialize('$str')) WITH ROLLUP WITH TOTALS FORMAT NULL"
+done