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burp repeater modifies some non printable characters to 0x3F

Ema | Last updated: May 05, 2022 10:58AM UTC

Hi. While performing a file upload of a pdf via the repeater, i noticed that before sending the request the repeater changes all characters with hex value in the range 0x80-0x9f to character 0x3f. Also i noticed this does not happen in all tabs, in one repeater tab the request is performed fine and characters are not changed, while in a different repeater tab in all requests from that tab the characters are modified as i described. In both cases the requests are exactly the same and content of the files was added using the "paste form file" option of the repeater, and in bot cases the file is inserted with the correct characters. However in one case when i select "send" i can se the characters being modified in the repeater and sent modified. there are no extensions enabled in the project. the requests have Content-Type: multipart/form-data. i would add a screenshot but i don't see the option here, however one example snipped would be "73 74 72 65 61 6D 0D 0A 78 [9C] A5 CD BD 0A" being modified to "73 74 72 65 61 6D 0D 0A 78 [3F] A5 CD BD 0A". thank you.

Hannah, PortSwigger Agent | Last updated: May 06, 2022 08:34AM UTC

Hi Could you drop us an email at support@portswigger.net with some further information, please? - The version of Burp you are using - If possible, the request that triggers this issue - Any screenshots of the issue

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