"summary":"If both the experimental ABIEncoderV2 and the experimental Yul optimizer are activated, one component of the Yul optimizer may reuse data in memory that has been changed in the meantime.",
"description":"The Yul optimizer incorrectly replaces ``mload`` and ``sload`` calls with values that have been previously written to the load location (and potentially changed in the meantime) if all of the following conditions are met: (1) there is a matching ``mstore`` or ``sstore`` call before; (2) the contents of memory or storage is only changed in a function that is called (directly or indirectly) in between the first store and the load call; (3) called function contains a for loop where the same memory location is changed in the condition or the post or body block. When used in Solidity mode, this can only happen if the experimental ABIEncoderV2 is activated and the experimental Yul optimizer has been activated manually in addition to the regular optimizer in the compiler settings.",
"summary":"Reading from calldata structs that contain dynamically encoded, but statically-sized members can result in incorrect values.",
"description":"When a calldata struct contains a dynamically encoded, but statically-sized member, the offsets for all subsequent struct members are calculated incorrectly. All reads from such members will result in invalid values. Only calldata structs are affected, i.e. this occurs in external functions with such structs as argument. Using affected structs in storage or memory or as arguments to public functions on the other hand works correctly.",
"summary":"Assigning an array of signed integers to a storage array of different type can lead to data corruption in that array.",
"description":"In two's complement, negative integers have their higher order bits set. In order to fit into a shared storage slot, these have to be set to zero. When a conversion is done at the same time, the bits to set to zero were incorrectly determined from the source and not the target type. This means that such copy operations can lead to incorrect values being stored.",
"summary":"Storage arrays containing structs or other statically-sized arrays are not read properly when directly encoded in external function calls or in abi.encode*.",
"description":"When storage arrays whose elements occupy more than a single storage slot are directly encoded in external function calls or using abi.encode*, their elements are read in an overlapping manner, i.e. the element pointer is not properly advanced between reads. This is not a problem when the storage data is first copied to a memory variable or if the storage array only contains value types or dynamically-sized arrays.",
"summary":"A contract's constructor that takes structs or arrays that contain dynamically-sized arrays reverts or decodes to invalid data.",
"description":"During construction of a contract, constructor parameters are copied from the code section to memory for decoding. The amount of bytes to copy was calculated incorrectly in case all parameters are statically-sized but contain dynamically-sized arrays as struct members or inner arrays. Such types are only available if ABIEncoderV2 is activated.",
"summary":"Calling uninitialized internal function pointers created in the constructor does not always revert and can cause unexpected behaviour.",
"description":"Uninitialized internal function pointers point to a special piece of code that causes a revert when called. Jump target positions are different during construction and after deployment, but the code for setting this special jump target only considered the situation after deployment.",
"summary":"Calling uninitialized internal function pointers created in the constructor does not always revert and can cause unexpected behaviour.",
"description":"Uninitialized internal function pointers point to a special piece of code that causes a revert when called. Jump target positions are different during construction and after deployment, but the code for setting this special jump target only considered the situation after deployment.",
"summary":"Storage structs and arrays with types shorter than 32 bytes can cause data corruption if encoded directly from storage using the experimental ABIEncoderV2.",
"description":"Elements of structs and arrays that are shorter than 32 bytes are not properly decoded from storage when encoded directly (i.e. not via a memory type) using ABIEncoderV2. This can cause corruption in the values themselves but can also overwrite other parts of the encoded data.",
"summary":"Storage structs and arrays with types shorter than 32 bytes can cause data corruption if encoded directly from storage using the experimental ABIEncoderV2.",
"description":"Elements of structs and arrays that are shorter than 32 bytes are not properly decoded from storage when encoded directly (i.e. not via a memory type) using ABIEncoderV2. This can cause corruption in the values themselves but can also overwrite other parts of the encoded data.",
"summary":"The optimizer incorrectly handles byte opcodes whose second argument is 31 or a constant expression that evaluates to 31. This can result in unexpected values.",
"description":"The optimizer incorrectly handles byte opcodes that use the constant 31 as second argument. This can happen when performing index access on bytesNN types with a compile-time constant value (not index) of 31 or when using the byte opcode in inline assembly.",
"summary":"Double bitwise shifts by large constants whose sum overflows 256 bits can result in unexpected values.",
"description":"Nested logical shift operations whose total shift size is 2**256 or more are incorrectly optimized. This only applies to shifts by numbers of bits that are compile-time constant expressions.",
"summary":"Using the ** operator with an exponent of type shorter than 256 bits can result in unexpected values.",
"description":"Higher order bits in the exponent are not properly cleaned before the EXP opcode is applied if the type of the exponent expression is smaller than 256 bits and not smaller than the type of the base. In that case, the result might be larger than expected if the exponent is assumed to lie within the value range of the type. Literal numbers as exponents are unaffected as are exponents or bases of type uint256.",
"summary":"Calling functions that return multi-dimensional fixed-size arrays can result in memory corruption.",
"description":"If Solidity code calls a function that returns a multi-dimensional fixed-size array, array elements are incorrectly interpreted as memory pointers and thus can cause memory corruption if the return values are accessed. Calling functions with multi-dimensional fixed-size arrays is unaffected as is returning fixed-size arrays from function calls. The regular expression only checks if such functions are present, not if they are called, which is required for the contract to be affected.",
"summary":"If a contract has both a new-style constructor (using the constructor keyword) and an old-style constructor (a function with the same name as the contract) at the same time, one of them will be ignored.",
"description":"If a contract has both a new-style constructor (using the constructor keyword) and an old-style constructor (a function with the same name as the contract) at the same time, one of them will be ignored. There will be a compiler warning about the old-style constructor, so contracts only using new-style constructors are fine.",
"summary":"It is possible to craft the name of a function such that it is executed instead of the fallback function in very specific circumstances.",
"description":"If a function has a selector consisting only of zeros, is payable and part of a contract that does not have a fallback function and at most five external functions in total, this function is called instead of the fallback function if Ether is sent to the contract without data.",
"summary":"The low-level .delegatecall() does not return the execution outcome, but converts the value returned by the functioned called to a boolean instead.",
"description":"The return value of the low-level .delegatecall() function is taken from a position in memory, where the call data or the return data resides. This value is interpreted as a boolean and put onto the stack. This means if the called function returns at least 32 zero bytes, .delegatecall() returns false even if the call was successful.",
"description":"The ecrecover precompile does not properly signal failure for malformed input (especially in the 'v' argument) and thus the Solidity function can return data that was previously present in the return area in memory.",
"description":"If the empty string literal \"\" is used as an argument in a function call, it is skipped by the encoder. This has the effect that the encoding of all arguments following this is shifted left by 32 bytes and thus the function call data is corrupted.",
"summary":"In some situations, the optimizer replaces certain numbers in the code with routines that compute different numbers.",
"description":"The optimizer tries to represent any number in the bytecode by routines that compute them with less gas. For some special numbers, an incorrect routine is generated. This could allow an attacker to e.g. trick victims about a specific amount of ether, or function calls to call different functions (or none at all).",
"summary":"Failure of the identity precompile was ignored.",
"description":"Calls to the identity contract, which is used for copying memory, ignored its return value. On the public chain, calls to the identity precompile can be made in a way that they never fail, but this might be different on private chains.",
"summary":"The optimizer did not properly reset its internal state at jump destinations, which could lead to data corruption.",
"description":"The optimizer performs symbolic execution at certain stages. At jump destinations, multiple code paths join and thus it has to compute a common state from the incoming edges. Computing this common state was simplified to just use the empty state, but this implementation was not done properly. This bug can cause data corruption.",
"severity":"medium",
"introduced":"0.4.5",
"fixed":"0.4.6",
"conditions":{
"optimizer":true
}
},
{
"name":"HighOrderByteCleanStorage",
"summary":"For short types, the high order bytes were not cleaned properly and could overwrite existing data.",
"description":"Types shorter than 32 bytes are packed together into the same 32 byte storage slot, but storage writes always write 32 bytes. For some types, the higher order bytes were not cleaned properly, which made it sometimes possible to overwrite a variable in storage when writing to another one.",
"summary":"The optimizer did not properly reset its knowledge about SHA3 operations resulting in some hashes (also used for storage variable positions) not being calculated correctly.",
"description":"The optimizer performs symbolic execution in order to save re-evaluating expressions whose value is already known. This knowledge was not properly reset across control flow paths and thus the optimizer sometimes thought that the result of a SHA3 operation is already present on the stack. This could result in data corruption by accessing the wrong storage slot.",
"summary":"Library functions threw an exception when called from a call that received Ether.",
"description":"Library functions are protected against sending them Ether through a call. Since the DELEGATECALL opcode forwards the information about how much Ether was sent with a call, the library function incorrectly assumed that Ether was sent to the library and threw an exception.",
"severity":"low",
"introduced":"0.4.0",
"fixed":"0.4.2"
},
{
"name":"SendFailsForZeroEther",
"summary":"The send function did not provide enough gas to the recipient if no Ether was sent with it.",
"description":"The recipient of an Ether transfer automatically receives a certain amount of gas from the EVM to handle the transfer. In the case of a zero-transfer, this gas is not provided which causes the recipient to throw an exception.",
"severity":"low",
"fixed":"0.4.0"
},
{
"name":"DynamicAllocationInfiniteLoop",
"summary":"Dynamic allocation of an empty memory array caused an infinite loop and thus an exception.",
"description":"Memory arrays can be created provided a length. If this length is zero, code was generated that did not terminate and thus consumed all gas.",
"summary":"The optimizer did not properly reset its internal state at jump destinations, which could lead to data corruption.",
"description":"The optimizer performs symbolic execution at certain stages. At jump destinations, multiple code paths join and thus it has to compute a common state from the incoming edges. Computing this common state was not done correctly. This bug can cause data corruption, but it is probably quite hard to use for targeted attacks.",
"severity":"low",
"fixed":"0.3.6",
"conditions":{
"optimizer":true
}
},
{
"name":"CleanBytesHigherOrderBits",
"summary":"The higher order bits of short bytesNN types were not cleaned before comparison.",
"description":"Two variables of type bytesNN were considered different if their higher order bits, which are not part of the actual value, were different. An attacker might use this to reach seemingly unreachable code paths by providing incorrectly formatted input data.",
"severity":"medium/high",
"fixed":"0.3.3"
},
{
"name":"ArrayAccessCleanHigherOrderBits",
"summary":"Access to array elements for arrays of types with less than 32 bytes did not correctly clean the higher order bits, causing corruption in other array elements.",
"description":"Multiple elements of an array of values that are shorter than 17 bytes are packed into the same storage slot. Writing to a single element of such an array did not properly clean the higher order bytes and thus could lead to data corruption.",
"severity":"medium/high",
"fixed":"0.3.1"
},
{
"name":"AncientCompiler",
"summary":"This compiler version is ancient and might contain several undocumented or undiscovered bugs.",
"description":"The list of bugs is only kept for compiler versions starting from 0.3.0, so older versions might contain undocumented bugs.",
