Fix a hard to find problem in DeviceRedirection #422
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Specifc file transfers would hang. A minimal reproducer was hard to create. It turns out that the issue was in the encapsulation of the TLSSecurityLayer. If a virtual channel packet at a specific length (0x80), it would confuse the next layer into thinking it was the Security Header's licensing bytes causing the payload to be skipped from its usual processing. See the recv() method of the TLSSecurityLayer class in `pyrdp/layer/rdp/security.py`. Turns out that the security layer is not required if we are using modern RDP access mechanisms (anything more recent than RC4) so we can just remove the layer when the MITM is setup. This fix happens to fix #139 as well.
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Specific file transfers would hang. A minimal reproducer was hard to create. It turns out that the issue was in the encapsulation of the TLSSecurityLayer. If a virtual channel packet has a specific length (0x80), it would confuse the next layer into thinking it was the Security Header's licensing bytes causing the payload to be skipped from its usual processing.
See the
recv()method of theTLSSecurityLayerclass inpyrdp/layer/rdp/security.py.Turns out that the security layer is not required if we are using modern RDP access mechanisms (anything more recent than RC4) so we can just remove the layer when the MITM is set up.
This fix happens to fix #139 as well.
Big shoutout to @xshill to help me dig for the root cause and fix the issue. Honorable mention to Flare Systems for letting me borrow him for one day last week.