fix(pdu): harden framing and empty output handling - #1515
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Marc-André Moreau (mamoreau-devolutions) merged 1 commit intoAug 2, 2026
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fix(pdu): harden framing and empty output handling#1515Marc-André Moreau (mamoreau-devolutions) merged 1 commit into
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Pull request overview
Hardens RDP frame validation while supporting zero-length empty output PDUs.
Changes:
- Rejects undersized TPKT and Fast-Path frames.
- Accepts empty Update and Pointer output PDUs with zero
totalLength. - Adds regression tests for malformed and compatible framing.
Reviewed changes
Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
crates/ironrdp-pdu/src/tpkt.rs |
Validates minimum TPKT size. |
crates/ironrdp-pdu/src/rdp/headers.rs |
Handles empty output PDUs and adds tests. |
crates/ironrdp-pdu/src/lib.rs |
Validates Fast-Path lengths and tests malformed frames. |
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Marc-André Moreau (mamoreau-devolutions)
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Marc-André Moreau (mamoreau-devolutions)
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Marc-André Moreau (mamoreau-devolutions)
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Reject Fast-Path and TPKT frames whose declared length is smaller than their header or minimum packet size. Also tolerate the zero-length `totalLength` variation used by empty Update and Pointer output PDUs, while continuing to reject zero-length non-output data PDUs. Adds regression coverage for malformed frame lengths and empty output compatibility. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>
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`ShareControlHeader::decode` rejects a Data PDU whose `totalLength` is smaller than the unit it decoded. That check costs whole sessions against VirtualBox VRDP, which declares 24 on a complete 8550-byte slow-path pointer update. `totalLength` is consulted here for exactly one purpose: locating trailing padding after the inner unit ([MS-RDPBCGR] 2.2.8.1.1.1.1). A value smaller than what was decoded therefore means there is no padding to skip, and nothing more. It is not grounds to reject the PDU — the inner unit already decoded within the cursor's bounds, and where the PDU ends is decided by the transport framing (the TPKT or fast-path length), never by this field. Deliberately narrow: a `totalLength` of zero stays rejected for anything but the no-op output PDUs Devolutions#1515 allowed. A field that is absent entirely is a different signal from one that is merely wrong, and Devolutions#1515 drew that line three days ago; this does not move it. All three of its tests still pass unchanged. Tests: the reporter's real frame shape (8565 bytes on the wire, 8550 of MCS user data, totalLength 24) now decodes; zero-length leniency is asserted not to have widened; over-declared padding is still consumed, and declared-but-absent padding still errors. Verified to fail — restoring the strict branch reddens the under-declared test and leaves the three guard tests green.
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Reject Fast-Path and TPKT frames whose declared length is smaller than their header or minimum packet size. Also tolerate the zero-length
totalLengthvariation used by empty Update and Pointer output PDUs, while continuing to reject zero-length non-output data PDUs.Adds regression coverage for malformed frame lengths and empty output compatibility.