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stringToBytes method outputting invalid/incorrect characters

AssistantX | Last updated: Dec 29, 2021 09:51PM UTC

First reported here https://github.com/synfron/ReshaperForBurp/issues/15#issuecomment-1002476347, a user reported that text they entered isn't being properly outputted in Burp Suite. It is outputting with invalid/incorrect characters that don't match the input. The user had the same issue with https://github.com/Hannah-PortSwigger/modifyResponse. After further investigation, it appears that the issue is actually with the stringToBytes method provided in the burp-extender-api library. The stringToBytes method doesn't seem to properly support texts of certain languages/ranges of characters. I have created a simplified example at https://pastes.io/raw/2sinn96odz. Note, in the example that the output text that was the result of decoding/re-encoding doesn't match the input text.

Hannah, PortSwigger Agent | Last updated: Jan 04, 2022 12:23PM UTC

Hi As detailed in the Extender API documentation, a character with the hex representation 0xWXYZ will always be converted into a byte with the representation 0xYZ. It performs the opposite conversion to the method bytesToString() (0xYZ -> 0x00YZ). This means that in cases where characters use multi-byte characters, there can be truncation of data leading to invalid/incorrect characters. - https://portswigger.net/burp/extender/api/burp/IExtensionHelpers.html#stringToBytes(java.lang.String) We have an ongoing request to modify this functionality. I can add your +1 to it if you would like?

AssistantX | Last updated: Jan 05, 2022 05:32AM UTC

How long has the change to bytesToString/stringToBytes been requested? What is the likelihood of this change being implemented? I ask this because I'd like my extension to be able to support languages with characters that are outside the 1 byte character spectrum and it would be helpful to know if I'd probably need to implement this myself if the API change is not likely to happen/is years off.

Hannah, PortSwigger Agent | Last updated: Jan 05, 2022 05:30PM UTC